Cell search for D2D enabled UEs in out of network coverage

ABSTRACT

There is disclosed a method for operating a D2D enabled UE for a cellular communication network. The method comprises performing a cell search in an out of coverage condition of the UE, wherein performing a cell search is based on a first measurement configuration during a first phase, and based on a second measurement configuration during a second phase, wherein the first measurement configuration pertains to a carrier whose sidelink is preconfigured for ProSe operation in out of network coverage operation. 
     The disclosure also pertains to related methods and devices.

TECHNICAL FIELD

The present disclosure pertains to the field of wireless communicationtechnology, in particular to D2D technology.

BACKGROUND

In wireless communication, D2D technology allows direct communicationbetween UEs, even if out of coverage of a network or base station.However, in out of coverage scenarios, a UE still has to perform cellsearch to re-establish cellular communication.

SUMMARY

An object of the present disclosure is to provide approaches allowingpredictable and well-defined cell search behaviour of a D2D enabled UEwhen it is out of coverage, and/or allowing quick cell search in such asituation.

Accordingly, there is disclosed a method for operating a D2D enabled UEfor a cellular communication network. The method comprises performing acell search in an out of coverage (OOC or ONC) condition of the UE.Performing a cell search is based on a first measurement configurationduring a first phase, and based on a second measurement configurationduring a second phase. The first measurement configuration pertains to acarrier whose sidelink is preconfigured for ProSe operation in out ofnetwork coverage operation.

Moreover, there is disclosed a D2D enabled UE for a cellularcommunication network. The D2D enabled UE is adapted for performing acell search in an out of coverage (OOC or ONC) condition of the UE,wherein performing a cell search is based on a first measurementconfiguration during a first phase, and performing a cell search isbased on a second measurement configuration during a second phase. Thefirst measurement configuration pertains to a carrier whose sidelink ispreconfigured for D2D operation in out of network coverage operation.

A method for operating a network node for a wireless communicationnetwork is also suggested. The method comprises configuring a D2Denabled UE with a first measurement configuration, wherein the firstmeasurement configuration pertains to a carrier whose sidelink ispreconfigured for D2D operation in out of network coverage operation.

There is also disclosed a network node for a wireless communicationnetwork. The network node is adapted for configuring a D2D enabled UEwith a first measurement configuration, wherein the first measurementconfiguration pertains to a carrier whose sidelink is preconfigured forD2D operation in out of network coverage operation.

Furthermore, a program product comprising code executable by controlcircuitry is proposed. The code causes the control circuitry to carryout and/or control any one of the methods for operating a user equipmentor network node as described herein.

Moreover, there is disclosed a carrier medium arrangement carryingand/or storing at least any one of the program products described hereinand/or code executable by control circuitry, the code causing thecontrol circuitry to perform and/or control at least any one of themethods described herein.

The approaches described herein facilitate quick (depending on theconditions) and well-defined cell search.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are provided to illustrate concepts and approaches of thedisclosure and are not intended as limitation. The drawings comprise:

FIG. 1, illustrating a scenario in which a D2D capable UE has lost itscoverage;

FIG. 2, showing UE cell detection in out of coverage as function oftime;

FIG. 3, showing an example of a UE handling of cell search in out-of-WANcoverage;

FIG. 4, showing an example of UE handling of Oscillator status withrespect to out-of-WAN coverage.

FIG. 5, schematically showing a user equipment;

FIG. 6, schematically showing a network node;

FIG. 7, showing a flowchart of a method for operating a D2D enabled UE;

FIG. 8, schematically showing a D2D enabled UE;

FIG. 9, showing a flowchart of a method for operating a network node;and

FIG. 10, schematically showing a network node.

DETAILED DESCRIPTION

UE measurements are discussed in the following.

Radio (UE) measurements done by the UE are typically performed on theserving as well as on neighbor cells over some known reference symbolsor pilot sequences. The measurements are done on cells on anintra-frequency carrier, inter-frequency carrier(s) as well as oninter-RAT carriers(s) (depending upon the UE capability whether itsupports that RAT). To enable inter-frequency and inter-RAT measurementsfor the UE requiring gaps, the network has to configure the measurementgaps.

The measurements are done for various purposes. Some example measurementpurposes are: mobility, positioning, self-organizing network (SON),minimization of drive tests (MDT), operation and maintenance (O&M),network planning and optimization etc. Examples of measurements in LTEare Cell identification aka PCI acquisition, Reference symbol receivedpower (RSRP), Reference symbol received quality (RSRQ), CGI acquisition,Reference signal time difference (RSTD), UE RX-TX time differencemeasurement, Radio link monitoring (RLM), which consists of Out ofsynchronization (out of sync) detection and In synchronization (in-sync)detection etc. CSI measurements performed by the UE are used forscheduling, link adaptation etc. by network. Examples of CSImeasurements or CSI reports are CQI, PMI, RI etc. They may be performedon reference signals like CRS, CSI-RS or DMRS.

Radio network node radio measurements are discussed in the following.

In order to support different functions such as mobility (e.g. cellselection, handover etc), positioning a UE, link adaption, scheduling,load balancing, admission control, interference management, interferencemitigation etc, the radio network node also performs radio measurementson signals transmitted and/or received by the radio network node.Examples of such measurements are SNR, SINR, received interference power(RIP), BLER, propagation delay between UE and itself, transmit carrierpower, transmit power of specific signals (e.g. Tx power of referencesignals), positioning measurements like TA, eNode B Rx-Tx timedifference etc.

Cell Search is discussed in the following.

The DL subframe #0 and subframe #5 carry synchronization signals (i.e.both PSS and SSS). In order to identify an unknown cell (e.g. newneighbor cell) the UE has to acquire the timing of that cell andeventually the physical cell ID (PCI). Subsequently the UE also measuresRSRP and/or RSRQ of the newly identified cell in order to use itselfand/or report the measurement to the network node. In total there are504 PCIs. Therefore the UE searches or identifies a cell (i.e. acquirePCI of the cell) by correlating the received PSS/SSS signals in DLsubframe #0 and/or in DL subframe #5 with one or more of the pre-definedPSS/SSS sequences. The use of subframe #0 and/or in DL subframe #5 forPCI acquisition depends upon its implementation. The UE regularlyattempts to identify neighbor cells on at least the serving carrierfrequenc(ies). But it may also search cells on non-serving carrier(s)when configured by the network node. In order to save UE powerconsumption, typically the UE searches in one of the DL subframes #0 and#5. In order to further save its battery power the UE searches the cellonce every 40 ms in non-DRX or in short DRX cycle (e.g. up to 40 ms). Inlonger DRX cycle the UE typically searches a cell once every DRX cycle.During each search attempt the UE typically stores a snapshot of 5-6 msand post process by correlating the stored signals with the knownPSS/SSS sequences. In non-DRX the UE is able to identify anintra-frequency cell (including RSRS/RSRQ measurements) within 800 ms(i.e. 20 attempts in total including 15 and 5 samples for cellidentification (PCI acquisition) and RSRP/RSRQ measurement).

D2D Operation is discussed in the following.

D2D enabled UEs generally transmit D2D signals or channels in the uplinkpart of the spectrum. D2D operation (which may also be called ProSecommunication; a D2D communication connection or link may also be calledsidelink) by a UE is in a half-duplex mode, i.e. the UE can eithertransmit D2D signals/channels or receive D2D signals/channels. There mayalso be D2D relay UEs that may relay some signals to other D2D enabledUEs. There is also control information for D2D, some of which istransmitted by D2D enabled UEs and the other is transmitted by ancontrol node or allocation node like an eNodeB (e.g., D2D resourcegrants for D2D communication transmitted via cellular DL controlchannels). The D2D transmissions may occur on resources which areconfigured by the network or selected autonomously by the D2D enabledUE.

D2D communication may imply transmitting by a D2D transmitter D2D dataand D2D communication control information with scheduling assignments(SAs) to assist D2D receivers of the D2D data. The D2D datatransmissions may be according to configured patterns and in principlemay be transmitted rather frequently. SAs are transmitted periodically.D2D transmitters that are within the network coverage (e.g. within aserving cell and/or in communication with a cellular network, e.g. viaan eNodeB) may request eNodeB resources for their D2D communicationtransmissions and receive in response D2D resource grants for SA and D2Ddata. Furthermore, eNodeB may broadcast D2D resource pools for D2Dcommunication.

D2D discovery messages are transmitted in infrequent periodic subframes.eNodeBs may broadcast D2D resource pools for D2D discovery, both forreception and transmission. It should be noted that in the context ofthis specification, eNodeB may be seen as an example for a network nodeor allocation node or control node and may me generalized accordingly.

The D2D communication may support two different modes of D2D operation:mode 1 and mode 2.

In mode 1, the location of the resources for transmission of thescheduling assignment by the broadcasting UE comes from the eNodeB. Thelocation of the resource(s) for transmission of the D2D data by thebroadcasting UE comes from the eNodeB.

In mode 2 a resource pool for scheduling assignment is pre-configuredand/or semi-statically allocated. The UE on its own selects the resourcefor scheduling assignment from the resource pool for schedulingassignment to transmit its scheduling assignment.

PCell interruption of 1 subframe occurs when UE switches its receptionbetween D2D-to-WAN or WAN-to-D2D. This is because the UE receiver chainneeds to be returned every time the operation is switched from WAN toD2D reception and from D2D to WAN reception. This applies to both D2Ddiscovery and D2D communication capable UEs. It is important topartition uplink resources between cellular uplink and D2D operation insuch a way that avoids or minimize the risk of switching taking place incertain subframe, subframe #0 and/or #5, of PCell. These subframescontain essential information such as PSS/SSS that are necessary fordoing cell search, carrying out cell measurements and they also containMIB/SIB1 information which is necessary for SI reading procedures. Inaddition to interruption that takes places due to switching, there maybe additional interruption of 1 subframe due to the RRC reconfigurationprocedure. While the switching interruption takes place for single rx UE(e.g. D2D discovery capable UEs), the RRC reconfiguration interruptiontakes place for all types of D2D enabled UEs (e.g. D2D Discovery capableand D2D Communication capable).

D2D operation is a generic term which may comprise transmission and/orreception of any type of D2D signals (e.g. physical signals, physicalchannel etc) by a D2D communication capable UE and/or by D2D discovercapable UE. D2D operation is therefore also called as D2D transmission,D2D reception, D2D communication etc, depending on which form ofoperation is performed.

A D2D enabled UE may also interchangeably be called ProSe capable UE. AD2D discovery capable UE is also referred to as UE capable of ProSedirect discovery and a D2D direct communication UE is also referred toas UE capable of ProSe direct communication. The link and/carrier thatis used for the D2D/ProSe direct communication and D2D/ProSe directdiscovery between UEs may be referred to as sidelink.

D2D operation in out of network coverage (ONC) is a new scenario. D2Denabled UEs can be pre-configured (e.g. by a network node and/or thenetwork, which may be correspondingly adapted) with ProSe resources thatthe UEs use when they are out of network coverage. Examples of ProSeresources are ProSe subframes, time slots, physical channels such asresource blocks within ProSE subframes or time slots etc. Thesepre-configured resources are intended to be used only in out of networkcoverage scenario. If they are used inside the cellular cells or inclose proximity of cellular cells, D2D enabled UEs may causeinterference and harm the cellular cells. To further minimizeinterference during ProSe operation in ONC operation, the D2D enabledUEs can further be configured with one or more parameters associatedwith the pre-configured ProSe resources. These parameters ensure that UEoperates with reduced power and lowers emissions in carriers outsidethat of the side link. Examples of these parameters associated withProSe resource parameters are P-Max-ProSe andadditionalSpectrumEmissions-ProSe. D2D enabled UE behavior on how thepre-configured ProSe resources shall be controlled when a new cell isdetected is not defined. Due to lack of UE behavior and correspondingperformance requirements, the use of ProSe resources by the D2D enabledUE when it enters inside the network coverage may cause interference tothe WAN i.e. where one or more WAN cells are operating and can receivesignals from the D2D enabled UE.

There are suggested methods and devices for cell detection for D2Denabled UEs in out of network coverage that can be implemented in D2Dcapable UEs.

An approach for operating a ProSe UE for detecting a cell and stoppingthe use of pre-configured resources for ProSe operation when the ProSeUE is in out of network coverage may comprise:

-   The ProSe UE upon entering in out of network coverage at time T1    until a first phase shall continuously detect cells belonging to:-   the intra-frequency of the last PCell within the existing    intra-frequency cell search delay defined as defined below, provided    that the UE has been in out of network coverage for not more than X    seconds,-   the inter-frequency carriers configured for measurements by the last    PCell within the existing inter-frequency cell search delay for gap    Id #0 defined below, provided that the UE has been in out of network    coverage for not more than Y seconds,-   the inter-RAT carriers configured for measurements by the last PCell    within the existing inter-RAT cell search delay for gap Id #0    defined in section below, provided that the UE has been in out of    network coverage for not more than Z seconds.-   If the UE is unable to detect any cell on the intra-frequency, the    configured inter-frequency or the configured inter-RAT carriers    during the first phase (i.e. within (T2−T1)=MAX (X, Y, Z) or in some    embodiment within (T2−T1)+(T3−T2), where (T3−T2)=MAX (X′, Y′, Z′)),    then the UE shall also continuously detect cells on carriers of all    frequency bands supported by the UE during a second phase. Where X′,    Y′ and Z′ are the durations for detecting intra-frequency,    inter-frequency and inter-RAT cells respectively.-   If the UE is able to detect any cell on the intra-frequency, the    configured inter-frequency or the configured inter-RAT carriers    during the first phase (i.e. within (T2−T1) or (T2−T1)+(T3−T2) in    some embodiments) on any other carrier, then the UE shall stop using    resources for ProSe pre-configured by the last PCell.-   If the newly detected cell during the first or the second phase    supports ProSe then the UE may use radio resources assigned by the    new cell for ProSe operation.

There is also discussed a method for operating a network node serving aProSe capable UE, comprising:

-   -   determining based on one or more criteria (e.g. UE band/RAT        capabilities) a first measurement configuration and a second        measurement configuration to be used by the ProSe UE for        detecting cells during the first phase and the second phase when        the UE operates in an out of network coverage;    -   configuring the UE with the determined first and the second        measurement configurations.

This approach enables the legacy UEs in the new cells to be served moreefficiently and quickly by only avoiding or reducing the interferencecaused by pre-configured ProSe resources on cells in the proximity ofthe UEs. Also, the protection of reception quality of one or more cellswhen ProSe UE is in ONC is facilitated. The cells may belong to anycarrier or RAT. The approach moreover enables D2D enabled UEs out ofnetwork coverage to more quickly find neighboring or new cells.

In some embodiments a general term “network node” is used, which cancorrespond to any type of radio network node or any network node adaptedfor or in communication with a UE and/or with another network node.Examples of network nodes are NodeB, MeNB, SeNB, a network nodebelonging to MCG or SCG, base station (BS), multi-standard radio (MSR)radio node such as MSR BS, eNodeB, network controller, radio networkcontroller (RNC), base station controller (BSC), relay, donor nodecontrolling relay, base transceiver station (BTS), access point (AP),transmission points, transmission nodes, RRU, RRH, nodes in distributedantenna system (DAS), core network node (e.g. MSC, MME etc), O&M, OSS,SON, positioning node (e.g. E-SMLC), MDT etc.

Also, in some cases the non-limiting term user equipment (UE) is used,which refers to any type of wireless device adapted for communicatingwith a network node and/or with another UE in a cellular or mobilecommunication system; the UE may be D2D enabled and/or adapted for outof coverage communication e.g. with another D2D enabled UE. Examples ofUEs are target device, device to device (D2D) UE, machine type UE or UEcapable of machine to machine (M2M) communication, PDA, PAD, Tablet,mobile terminals, smart phone, laptop embedded equipped (LEE), laptopmounted equipment (LME), USB dongles etc.

In some embodiment term out of coverage (OOC) is used. OOC may alsointerchangeably be called as out-of-network (ONC) coverage, out of WANcoverage, out of cellular coverage, any cell selection state etc. Inthis scenario D2D enabled UEs communicating with each other are notunder network node coverage. It means that the D2D enabled UEs cannotreceive signals from and/or transmit signals to any network node in the(or any) network using cellular communication. Typically, the lack ofcoverage (OOC) is due to complete absence of the network coverage in thevicinity of the D2D enabled UE, e.g. due to weak or non-existent signals(or the UE in question not yet being aware that it has entered coverageagain, e.g. due to not having performed a successful cell searchprocedure). Thus, the D2D enabled UEs cannot use timing and frequencysynchronization based on signals from any cell in the network. It such acondition, the UE may perform cell search

The embodiments are described for LTE. However the embodiments areapplicable to any RAT or multi-RAT systems, where the UE receives and/ortransmit signals (e.g. data) e.g. LTE FDD/TDD, WCDMA/HSPA, GSM/GERAN, WiFi, WLAN, CDMA2000 etc.

Some embodiments are described as:

-   -   General description of a scenario    -   A method in a D2D enabled UE in out of network coverage for        performing cell identification procedure    -   A method in a network node configuring a D2D enabled UE with        carrier/s for cell detection in out of network coverage

A general scenario description is provided in the following.

A scenario may comprise at least one network node serving a first cell,say PCell (Primary Cell) aka serving cell. The D2D capable UE (which mayalso be called D2D enabled UE or ProSe enabled UE, or short D2D UE orProSe UE, or even shorter just UE) can be pre-configured by the PCell(respectively, by the network node via the PCell) with ProSe resourcesfor ProSe operation of the D2D ENABLED on a sidelink. The pre-configuredProSe resources may in particular be used by the D2D enabled UE whenoperating in ONC. The sidelink may typically operate on a carrier of thePCell (aka serving carrier frequency or intra-frequency carrier). Thesidelink may also be configured for ProSe operation on a non-servingcarrier of the D2D enabled UE e.g. inter-frequency carrier frequency forWAN measurements or carrier frequency only configured for ProSeoperation.

In some embodiments the D2D capable UE may also be configured withanother cell that is configurable upon need basis, say SCell1 (SecondaryCell 1). In some embodiment the SCell1 may be served by a second networknode. The embodiments apply regardless of whether PCell and one or moreSCells are served by the same or different network nodes. In this case,the D2D capable UE can be pre-configured, e.g., by the network node)with ProSe resources for ProSe operation on sidelink which may operateon carrier of PCell or of SCell or of any non-serving carrier. The D2Dcapable UE can be pre-configured with ProSe resources for ProSeoperation on plurality of sidelinks, e.g. carriers of PCell, SCell1 andnon-serving carrier.

The network node may also configure the D2D capable UE with a thirdcell, SCell2 on a different carrier on need basis. The embodimentspresented in this description apply for UE configured with CA (CarrierAggregation) with any number of SCells. In some embodiments the UE maybe configured with PCell and PSCell (Primary Secondary Cell) or withPCell, PSCell and one or more SCells such as in dual connectivity. Theconfigured cells are UE specific and the embodiments included in thisdisclosure may be applied on UE basis on the each configured cell.

There may typically be two types of UEs in the network; the first type,type 1, being the cellular capable UE operating cellular traffic aka WANcapable UE or legacy UE. The second type, type 2, of UE is the D2Dcapable UE, which are also capable of cellular operation. The type 2 canbe configured to operate for only WAN traffic in case D2D operation isnot required. The UEs can be configured to operate on any cells. Theembodiments apply when at least one type 2 UE is available in thenetwork. Such a UE can be configured with at least one SCell. The PCell,PSCell and SCell(s) are UE specific. However plurality of UEs can beconfigured with the same cell as their PCell or SCell or PSCell.Therefore typically a group of UEs may have the same PCell, which isdifferent than the PCell of another group of UEs.

The D2D enabled UE is able to operate some D2D operations while beingout of network coverage. Examples of such operations are D2DCommunication, D2D discovery etc. They may further comprise of D2Dtransmission, D2D reception etc. FIG. 1 illustrates the scenario inwhich a D2D capable UE has lost its coverage to an old PCell (Cell 1)and is searching for a new cell (Cell 2). The D2D enabled UE configuredwith one or more SCells, may have lost all serving cells to be in ONCi.e. lost PCell and SCell(s).

While being out of network coverage, the D2D enabled UE (UE A) issynchronized with another D2D capable UE (UE B) and it performs D2Dcommunication. The synchronization herein means that the UE-A uses UE-Bas the timing source (aka synchronization) for transmitting D2D signals.The presented solution addresses the problem of UE A in this scenarioharming (causes interference) on Cell 2 due to that the UE A performsD2D operation using the pre-configured with ProSe resources foroperation in out of network coverage.

Prior to entering in ONC, the D2D enabled UE may also be configured bythe last serving cell (e.g. PCell and/or SCell(s)) with one or morecarriers for doing measurements on the cells of the configured carriers.The D2D enabled UE may be configured with such carrier(s) for measuringin idle state and/or in connected state. The UE may also bepreconfigured with one or more carriers specifically for D2D operationin ONC. In some embodiments these D2D specific carriers may be the sameas the serving carriers. The same or different set of carriers may beconfigured for measurements in idle state and connected state. Examplesof such carriers are serving carriers (e.g. intra-frequency aka servingcarrier, PCC, SCC(s) PSCC etc) and non-serving carriers (e.g.inter-frequency carriers, inter-RAT carriers etc).

A method in a D2D enabled UE in out of network coverage for performingcell identification procedure is described in the following.

This embodiment discloses a method for operating (and/or being carriedout or implemented in) a D2D capable UE (as well as a correspondinglyadapted UE), wherein the UE may be out of network coverage or in theprocess of entering such a state. According to the method, the D2Dcapable UE may adapt its cell search procedure based on whether the UEis pre-configured with ProSe resources or not. Resources may bepre-configured using some parameters that are configured forout-of-coverage scenarios. Examples of such parameters are ProSesubframes, time slots, physical channels such as resource blocks withinProSE subframes or time slots etc. The D2D enabled UE may also beconfigured by the network node, e.g. using higher layer signaling, withone or more emission control parameters such as maximum power etc. TheD2D enabled UE may apply the emission control parameters whentransmitting ProSe signaling using pre-configured ProSs resources forProSe operation in ONC. Specific examples of emission control parametersare:

-   P-Max-ProSe; parameter used to limit the maximum transmit power when    the ProSe UE operates in out-of-coverage.-   additionalSpectrumEmissions-ProSe; parameter used to adjust the    transmission to meet the region-specific regulatory emission    requirements when ProSe UE operates in out-of-coverage.

The pre-configured ProSe resources in the vicinity of a new cellularcell or when it detects a new cell on the cellular carrier while beingin ONC may cause issues explained below.

The duration during the ProSe UE is out of network coverage may vary andthe new cell which the ProSe UE detects may be of various types. The D2Denabled UE in out-of-coverage may for example detect a cell onintra-frequency, configured inter-frequency or configured inter-RATcarriers or any non-configured carrier. ProSe may or may not besupported by the new cell, respectively the corresponding network node.

The new cell may be victim to ProSe interference from the timepre-configured resources are used until the new cell is detected. Butalso from the time the new cell is detected and till the time thepre-configured resources are not disabled.

When the ProSe UE is camped on a cell or it has a serving cell (PCell),then the ProSe UE should use the radio resources indicated by its PCell.These are indicated by the network node (e.g. eNB) using the SIB ordedicated signaling. If ProSe UE continues to use the pre-configuredradio resources which were derived particularly for the out-of-coveragescenario in in-coverage scenario, this may result in that the ProSeharming the cellular network. The victim cell may for example be a cellon intra-frequency, configured inter-frequency or configured inter-RATcarriers or any non-configured carrier. ProSe may or may not besupported by that new cell.

A ProSe UE which is out of network coverage is required to scan for newcellular cells that it can connect to. The ProSe UE can be out ofnetwork coverage for different periods, and the length of this periodaffects the total cell search delay. For example, if the ProSe UE hasbeen out-of-coverage for very short time and it detects a cellular cell,then some of the old configurations may still be valid, e.g. frequency-and time synchronization. On the contrary, if the ProSe UE has beenout-of-coverage for long time, the frequency- and time synchronizationmay have changed or the old configurations may not be valid any longer.This may lead to longer cell search time. There is suggested to define atime or time difference (e.g., X or Δ1 or Δt1), up to which the ProSe UEremembers its old receiver configuration, which may be called athreshold or memory time. And this time may be different for thedifferent type of cells (or in other words, there may be defineddifferent such times for different types of cells and/or applications).Instead of one time per configuration, there may be defined more thanone times or thresholds associated to different phases. Examples of suchconfigurations (in particular corresponding to a measurementconfiguration, which may be a first measurement configuration) are:

Time and frequency configuration and/or

Intra-band center-frequency location and/or

Supported band configuration.

It should be noted that a configuration for receiving and/orcommunicating in a cell may be basis for and/or equivalent to ameasurement configuration, in particular if it is re-used and/orremembered for measuring.

Such a configuration may in particular comprise settings of a receiverand/or receiver circuitry, e.g. a corresponding oscillator.

Remembering these receiver configurations (e.g., by keeping them in amemory and/or keeping the corresponding circuitry/subsystems, like e.g.receiver and/or measurement system, in the respective configuration, ifapplicable) will lead to reduced cell search time up to a certain timeat the ProSe UE. Consequently, this may reduce the time during which thenew cell is subject to interference by the ProSe UE.

The following subsections discuss the UE cell search procedure (aka celldetection procedure, cell identification procedure etc) when the cellsto be detected may belong to different carriers, e.g. configured andnon-configured. There may be two different embodiments related to UEcell search procedure in ONC:

-   Detection of cells on configured carriers and non-configured    carriers in series by ProSe UE in out of network coverage-   Detection of cells on configured carriers and non-configured    carriers over at least partly parallel time by ProSe UE in out of    network coverage

Detection of cells by ProSe UE on configured carriers and non-configuredcarriers in series is discussed in the following.

In this variant, the UE first attempts to detect cells on any of thecarriers configured by the UE's last PCell before the UE entered in ONC(which may be referred to as configured carriers). Examples of suchcarriers are last intra-frequency (i.e. carrier of the last PCell beforeUE entered in ONC), carrier(s) whose sidelink(s) are preconfigured forProSe operation in out of network coverage operation, last configuredinter-frequency carriers and inter-RAT carriers. In some embodiment thelast intra-frequency and carrier(s) whose sidelink(s) are configured forProSe operation in ONC may be the same. However in some embodiment thelast intra-frequency and carrier(s) whose sidelink(s) are configured forProSe operation in ONC may be different. The UE may be explicitlyconfigured with the information about the configured carriers (e.g., bythe corresponding network node). For example, the UE may be configuredwith one or more carrier frequency channel numbers aka EARFCN.

If no cell (in particular a cell using one of the configured carriers)is detected up to certain time in a first phase (which may be defined bya first time threshold, which in turn may define the end of the firstphase, and may be defined/referred to as X or delta1 or T2), then the UEduring a second phase (which may be defined by a second time threshold,e.g. Y or T2 or a corresponding time difference, e.g. delta2 identifyingthe end of the second phase; the beginning may be defined by the firsttime threshold) starts the detection of cells on all non-configuredcarriers on all bands supported by the UE. All carriers are treated asnon-configured carriers during the second phase i.e. including the lastconfigured carriers. These aspects are described in detail in thefollowing sections. Both phases may be determined from a commonbeginning time (e.g. T1 and/or the time when an ONC condition begins/isdetected or determined), wherein the respective time thresholds may bedefined by suitable difference terms, e.g. delta1 and/or delta2.

Detection of new cells by ProSe UE in out of network coverage whilemeasurement configurations are valid is discussed in the following.

In this first example, it is assumed that the newly detected cell is anintra-frequency cell. For example, it can be the same old serving cellProSe UE was connected to before going to ONC or it can also be a newcell. The old serving cell may also be called as the last serving cell.In order to detect the new cell, the UE receiver has to first find thelocation of center frequency and then detect the PSS/SSS in 6 RBslocated in the center frequency. The center-frequency of allintra-frequency cells (i.e. cells on the carrier of the last servingcell) is located in the same position in frequency domain i.e. have thesame EARFNC. Thus the new cell is detected quicker provided that the oldmeasurement configuration is kept within the UE at this point in time,i.e. the old receiver configurations are still applicable.

The receiver configuration may also be interchangeably calledmeasurement configuration. The old measurement configuration may becomeinvalid or unreliable or irrelevant because for example the UE can storesuch information for a limited amount of time due to limited memory.Another reason is that due to UE mobility the timing information may notbe valid. Yet another reason is that the cell transmit timing may driftover time and/or cell transmit frequency may drift wrt storedsynchronization information at the UE.

FIG. 2 illustrates the events in a time-axis of a ProSe UE in an examplescenario. At time T1, the UE loses its connection to PCell, i.e. it goesout of network coverage. T2 is the point in time when the UE loses itsold receiver configuration or at which the old receiver configurationsbecome invalid. The receiver configuration herein means for exampleinformation about the last serving carrier frequency (e.g. EARFNC), timesynchronization to the last serving cell, synchronization to the lastserving cell or to the last serving carrier frequency etc. If the UE hasbeen out-of-coverage for long time, e.g. time greater than Δ1, that theold measurement configuration is not valid or lost, then the cell searchprocedure may take longer time and it may correspond to initial cellsearch procedure.

If the UE has been out of network coverage for not more than X seconds,wherein Δ1≦X s, cell search of a cell on the last intra-frequencycarrier could be prioritized. X is the time during which theintra-frequency receiver configurations are valid. By prioritizingintra-frequency cell search with measurement configurations over otherswith no measurement configurations the target cell may be detectedfaster compared to the case if the old cell configurations are notvalid.

In some embodiments the UE can detect the cell within X seconds e.g. ifradio conditions are favorable such as SINR of the cell is above orequal to a threshold (e.g. −3 dB). However in some embodiments the UEcan detect the cell within X′ seconds, where X′ is the duration startingfrom T2 i.e. just after duration X. This may be the case when the UEstarts detecting the cell at the end of the duration of X or when theradio conditions of the cell are not very favorable such as SINR of thecell is below a threshold (e.g. −3 dB). In some embodiments the durationX′ may further be scaled with the total number of configured carriers(N_(freq) _(_) _(X)). Example of such scaling of the duration is:X′*N_(freq) _(_) _(X). Example of the total number of configuredcarriers (N_(freq) _(_) _(X)) is the sum of the intra-frequency/servingcarrier(s), inter-frequency carriers and/or inter-RAT carriersconfigured for measurements by the old serving cell.

In a second example, it is assumed that Δ1≦Y where Y is the time duringwhich inter-frequency receiver configurations are valid. In this case,cell detection on any of the inter-frequency configured by the lastPCell may be prioritized over cell search that lacks any priorknowledge. This may also lead to that the candidate cells are detectedfaster and interference caused by pre-configured ProSe may be reduced.The inter-frequency cell detection is generally performed usingmeasurement gaps. Typical length of measurement gap is 6 ms. However, aProSe UE which is already out of network coverage may be able to performcell detection using without gaps.

However the time to detect the inter-frequency cell can be based on orderived using certain measurement gap configuration e.g. based onmeasurement gap configuration #0, i.e. with no gaps. In some embodimentsthe UE can detect the inter-frequency cell within Y seconds e.g. ifradio conditions are favorable such as SINR of the inter-frequency cellis above or equal to a threshold (e.g. −3 dB). However in someembodiments the UE can detect the inter-frequency cell within Y′seconds, where Y′ is the duration starting from T2 i.e. just afterduration Y. This may be the case when the UE starts detecting theinter-frequency cell at the end of the duration of Y or when the radioconditions of the inter-frequency cell are not very favorable such asSINR of the inter-frequency cell is below a threshold (e.g. −3 dB). Insome embodiments the duration Y′ may further be scaled with the totalnumber of configured carriers (N_(freq) _(_) _(Y)). Example of suchscaling of the duration is: Y′*N_(freq) _(_) _(Y). Example of the totalnumber of configured carriers (N_(freq) _(_) _(Y)) is the sum of theinter-frequency carriers and/or inter-RAT carriers configured formeasurements by the old serving cell. Example of the total number ofconfigured carriers (N_(freq) _(_) _(Y)) is the sum of theintra-frequency/serving carrier(s), inter-frequency carriers and/orinter-RAT carriers configured for measurements by the old serving cell.

A third example considers the case of an inter-RAT cell detection whereΔ1<=Z s. It is assumed that Z is the time during which the old PCellconfigurations on inter-RAT carriers are valid. In this case, cellsearch with prior-knowledge of inter-RAT carriers or receiverconfigurations may be prioritized over cell search with noprior-knowledge. Similar to inter-frequency cell search procedure, thecell search procedure could be performed using no measurement gapsconfiguration #0 since the ProSe UE is already out of network coverage.In some embodiments the UE can detect the inter-RAT cell within Zseconds e.g. if radio conditions are favorable such as SINR of theinter-frequency cell is above or equal to a threshold (e.g. −3 dB).However in some embodiments the UE can detect the inter-RAT cell withinZ′ seconds, where Z′ is the duration starting from T2 i.e. just afterduration Z. This may be the case when the UE starts detecting theinter-RAT cell at the end of the duration of Z or when the radioconditions of the inter-RAT cell are not very favorable such as SINR ofthe inter-RAT cell is below a threshold (e.g. −3 dB). In someembodiments the duration Z′ may further be scaled with the total numberof configured carriers (N_(freq) _(_) _(Z)). Example of such scaling ofthe duration is: Y′*N_(freq) _(_) _(Z). Example of the total number ofconfigured carriers (N_(freq) _(_) _(Z)) is the sum of theinter-frequency carriers and/or inter-RAT carriers configured formeasurements by the old serving cell. Example of the total number ofconfigured carriers (N_(freq) _(_) _(Z)) is the sum of theintra-frequency/serving carrier(s), inter-frequency carriers and/orinter-RAT carriers configured for measurements by the old serving cell.

In some embodiments the scaling factors N_(freq) _(_) _(X), N_(freq)_(_) _(Y) and N_(freq) _(_) _(Z) may be the same i.e. N_(freq)=N_(freq)_(_) _(X)=N_(freq) _(_) _(Y)=N_(freq) _(_) _(Z).

Regardless of the newly detected cell type (intra-freq., inter-freq.,inter-RAT, or any other carrier), the ProSe UE shall stop using thepre-configured ProSe resources as it detects a new cell which may belongto any of the old serving carrier(s), configured inter-frequencycarrier(s) and configured inter-RAT carrier(s) by the last serving cell.This may result in that the new cell is not harmed or less subject tointerference due to the pre-configured ProSe resources.

The UE in ONC may typically detect cells on old serving carrier(s),configured inter-frequency carrier(s) and configured inter-RATcarrier(s) in parallel or around the same time. For example over aduration Δ1=MAX(X,Y,Z), the UE may attempt to detect cells on oldserving carrier(s), configured inter-frequency carrier(s) and configuredinter-RAT carrier(s).

However in another exemplary embodiment the UE in ONC may detect cellson old serving carrier(s), configured inter-frequency carrier(s) andconfigured inter-RAT carrier(s) in serial order. Example of such orderis detecting cells first on serving carrier, then on inter-frequencycarriers if no cell is detected on serving carrier(s) and finally oninter-RAT carrier(s) if no cell is detected on inter-frequencycarrier(s).

In yet another exemplary embodiment the UE in ONC may detect cells onold serving carrier(s), configured inter-frequency carrier(s) andconfigured inter-RAT carrier(s) according to pre-defined order e.g.first on old serving carrier then on inter-RAT carriers and finally oninter-RAT carriers.

In yet another exemplary embodiment the UE in ONC may typically detectcells on old serving carrier(s), configured inter-frequency carrier(s)and configured inter-RAT carrier(s) according to the order configured bythe network node e.g. by the last serving cell.

Detection of new cells by ProSe UE in out of network coverage aftermeasurement configurations expires is discussed in the following.

If the ProSe UE has been out-of-coverage for long time (e.g. more than 5s) then the UE may not be able to “remember” the old receiverconfigurations or the configurations may not be valid any longer. Inthat case the cell search procedure becomes similar to initial cellsearch whose requirements are not specified in the standard. In thiscase, the ProSE UE may search for cells on all supported frequency bandsi.e. within each band it will search cells. For example in LTE the UEmay have to detect PSS/SSS in every 100 KHz (channel raster). If PSS/SSSis detected then it knows where the centre frequency is because PSS/SSSare transmitted in the centre frequency and it will align its frequency-and time-synchronization towards that new cell.

This embodiment considers the case when the ProSe UE has been out ofnetwork coverage for long time which has resulted in that themeasurement configuration of the intra-frequency, the inter-frequency orthe inter-RAT carriers have expired. When the configuration expires, theUE shall perform initial cell search for cells belonging to carriers ofall its supported bands.

As an example, if the UE has been out of network coverage for a giventime, e.g. Δ1 seconds, where Δ1>MAX(X,Y,Z), then the UE may choose toperform cell search on carriers of all its supported bands.

In another example, if the UE has been out of network coverage for Δ1seconds, where Δ1>MAX(X, Y, Z), then the UE may choose to perform cellsearch of cells on carriers of one or specific set of supported bandsi.e. perform initial cell search.

In yet another example, if the UE has been out of network coverage forΔ_(Total)=Δ1+Δ2 seconds, where Δ1>=MAX(X, Y, Z) and Δ2>MAX(X′, Y′, Z′),then the UE may choose to perform cell search of cells on carriers ofone or specific set of supported bands.

In yet another example, if the UE has been out of network coverage forΔ1+Δ2 seconds, where Δ1>MAX(X, Y, Z) and Δ2>MAX(X′ *N_(freq) _(_) _(X),Y′ *N_(freq) _(_) _(Y), Z′ *N_(freq) _(_) _(Z)), then the UE may chooseto perform cell search of cells on carriers of one or specific set ofsupported bands.

In yet another example, if the UE has been out of network coverage forΔ1+Δ2 seconds, where Δ1>MAX(X, Y, Z) and Δ2>MAX(X′, Y′ *N_(freq) _(_)_(Z), Z′ *N_(freq) _(_) _(Z)), then the UE may choose to perform cellsearch of cells on carriers of one or specific set of supported bands.

The specific set of bands whose carriers are searched for may bepre-defined, UE implementation specific or configured by the networknode. The UE may detect first cells of certain RAT e.g. first LTE cellsand if no LTE cell is detected then the UE may detect cells of otherRATs such as UMTS. The order in which the UE should detect cells ofdifferent RATs after the duration Δ1 may also be pre-defined, UEimplementation specific or configured by the network node.

In an another example, if the UE has been out of network coverage for Δ1seconds, where Δ1>=X and Δ1>=Z but Δ1<=Y, then the UE may perform cellsearch firstly on inter-frequency carriers using the measurementconfigurations configured at last PCell.

The duration Δ1=MAX(X, Y, Z) or Δ_(Total)=Δ1+Δ2 may also be called as afirst phase of cell detection i.e. when UE attempts to detect a cell onany of the old serving carrier(s), configured inter-frequency or theconfigured inter-RAT carriers.

Where Δ2=MAX(X′, Y′, Z′) or Δ2=MAX(X′ *N_(freq) _(_) _(X), Y′ *N_(freq)_(_) _(Y), Z′ *N_(freq) _(_) _(Z)),

The duration Δ3 which starts after the first phase may be called as asecond phase of cell detection. During the second phase as stated abovethe UE detects the cell using initial cell search procedure on carriersof one or more supported bands of the UE.

The second phase of cell detection may further be scaled with the totalnumber of carriers to search for in all bands where search is done bythe UE e.g. Δ3′=Δ3*N_(carriers) _(_) _(total)) where Δ3′ is the scaledvalue of the second phase. The N_(carriers) _(_) _(total) may correspondto all carriers of all RATs searched by the UE for detecting a cellduring the second phase.

Detection of cells by ProSe UE on configured carriers and non-configuredcarriers over partly overlapping time is discussed in the following.

In this embodiment the UE also first attempts to detect cells on any ofthe carriers configured by the UE's last PCell before the UE entered inONC. If no cell is detected up to certain time in the first phase thenthe UE during the second phase starts the detection of cells on lastconfigured carriers as well as non-configured carriers on all bandssupported by the UE. The key difference is that in this embodiment, theUE treats the last configured carrier and non-configured carriersseparately for cell detection during the second phase. These aspects aredescribed in detail below.

The UE starts identifying a cell on at least one of the configuredcarriers (i.e. configured by the last PCell) upon entering into ONC.Examples of such carriers are last intra-frequency, carrier(s) whosesidelink(s) are configured for ProSe operation in ONC, last configuredinter-frequency carriers and inter-RAT carriers. In some embodiment thelast intra-frequency and carrier(s) whose sidelink(s) are configured forProSe operation in ONC may be the same. However in some embodiment thelast intra-frequency and carrier(s) whose sidelink(s) are configured forProSe operation in ONC may be different. The UE is typically explicitlyconfigured with the information about the configured carriers. Forexample the UE is configured with the carrier frequency channel numberaka EARFCN. The UE may also be explicitly indicated whether a particularpreconfigured carrier is using or will use D2D operation or not. Forexample an operator A may inform the UE about the carriers used for D2Doperation in the operator B network. This will enable the UE to identifycells on the carrier(s) of the operator B when roaming into the operatorB network coverage. The UE can then also use D2D resources for D2Doperation in operator B network.

Typically the UE may start identifying a cell on all the configuredcarriers (e.g. at different time).

In some embodiment the UE may identify the cells on the lastintra-frequency and the carrier preconfigured with D2D operation in ONCover the same time period i.e. identifying a cell by sharing the timeresources between the two types of carriers. For example UE may identifya cell on one last intra-frequency and one carrier preconfigured withD2D operation within 2*Tintra_identify; where Tintra_identify time toidentify a cell on intra-frequency carrier.

In some embodiment the UE may identify the cells on the configuredinter-frequency carriers and the carrier preconfigured with D2Doperation in ONC over the same time period i.e. identifying a cell bysharing the time resources between the two types of carriers. Forexample UE may identify a cell on one inter-frequency and one carrierpreconfigured with D2D operation within 2*Tinter_identify; whereTinter_identify time to identify a cell on inter-frequency carrier.

The UE procedures related to this embodiment are summarized below. Theseprocedures may be pre-defined and the UE has to comply to these rules.

-   Cell detection during the first phase:-   If the UE has been in ONC for not more than certain time period    (Tmax, Tmax1 or X or T1+delta1, or T2, depending on the terminology    used) (e.g. less than or equal to 5 seconds) and a cell on a    configured carrier is detectable, then the UE may identify the cell    within a first time period. A cell is considered detectable provided    it meets the cell identification conditions. Examples of such    conditions are the received signal quality and signal strength    levels at the UE. As an example the first time period is the    measurement period (Tperiod) of the measurement on the detectable    cell e.g. 200 ms for RSRP/RSRQ measurement. In another example the    first time period may be multiple of the basic measurement period    e.g. 4*Tperiod. In another example the first time period may be    multiple of the measurement period if the UE has to identify cells    on multiple carriers e.g. 2*Tperiod if there are two configured    carriers. Examples of signal quality and signal strengths related    conditions for intra-frequency cells are SINR (e.g. −6 dB) and RSRP    (e.g. −120 dBm) respectively.-   In some embodiment the UE may identify the cell during the first    time period provided one or more additional conditions related to    the cell to be identified are also met. Examples of such conditions    are the change in the timing of the cell, frequency offset or change    in the frequency of cell since it was last measured by the UE. For    example the UE may identify the cell within the first time period    provided the timing of the cell has not changed by more than ±50 Ts    (Ts=32.5 ns) since it was last measured. In another example the UE    may identify the cell within the first time period provided the    carrier frequency of the cell has not changed by more than ±100 Hz    since it was last measured.-   Cell detection during the second phase:-   If the UE has been in ONC for more than certain time period (e.g.    more than 5 seconds) and a cell on the configured carrier is    detectable then the UE identifies the cell within a second time    period. As an example the second time period is the cell    identification time e.g. 800 ms for identification of the    intra-frequency cell, about 3 seconds for identification of the    inter-frequency cell etc. In another example the second time period    may be multiple of cell identification time (Tidentify) e.g.    3*Tidentify. In yet another example the second time period may be    multiple of Tidentify if the UE has to identify cells on multiple    carriers e.g. 2*Tidentify for two configured carriers. In a    preferred embodiment the first time period is shorter than the    second time period. However in some embodiments they may be the    same.-   Also in some embodiment the UE may identify the cell during the    second time period provided one or more additional conditions    related to the cell to be identified are also met. Examples of such    conditions are the change in the timing of the cell, frequency    offset or change in the frequency of cell since it was last measured    by the UE. For example the UE may identify the cell within the    second time period provided the timing of the cell has not changed    by more than ±100 Ts (Ts=32.5 ns) since it was last measured. In    another example the UE may identify the cell within the second time    period provided the carrier frequency of the cell has not changed by    more than ±200 Hz since it was last measured.-   In some embodiments it may also be pre-defined that regardless of    the time during which the UE has been in ONC and a cell on the    configured carrier is detectable then the UE identifies the cell    within a second time period. On this case the UE may identify the    cell during the second time period provided one or more additional    conditions related to the cell to be identified are also met as    elaborated above.-   If the UE has been in ONC for more than certain time period (e.g. 6    seconds or more) and if the UE has not detected any cell on any    configured carrier then the UE continue detecting the cell on the    configured carrier(s) within the second time period. But in addition    the UE also start identifying cells on non-configured carriers which    belong to the bands supported by the UE. The non-configured carriers    herein refer to the carriers which are not configured by the last    PCell of the UE before it enters into the ONC. The UE may identify a    cell on the non-configured carriers during a third time period. The    third time period the UE may typically be longer than the first and    the second time periods.-   If the UE identifies any cell on any of the configured carriers    (e.g. intra-frequency carrier(s), carrier(s) configured with D2D    operation in ONC, the configured inter-frequency carriers, the    configured inter-RAT carriers etc) or any of the non-configured    carriers belonging to the supported bands (i.e. during any of the    first or second phases) then:-   the UE may stop using the preconfigured resources for ProSe    operation on any of the carrier and-   the UE may also use resources assigned by the newly identified cell    for ProSe operation on the slidelink on the carrier of the newly    identified cell.

The above procedure is also described with an example:

Assume the UE currently in ONC was configured with:

-   an intra-frequency whose sidelink was used for ProSe operation by    the UE,-   one inter-frequency carrier and-   one inter-RAT carrier (e.g. UTRA FDD carrier).

The UE starts identifying cells on the intra-frequency, theinter-frequency carrier and the inter-RAT carrier when the UE enters inthe ONC. If the UE is unable to detect any cell on any of the threecarriers until a total duration of Tmax_total then the UE also startsidentifying a cell on other carriers (i.e. non-configured carriers)belonging to the bands supported by the UE. If the UE detects cell onany of the configured or non-configured carriers then the UE stops usingthe preconfigured ProSe resources for ProSe operation. The UE may alsoacquire new set of ProSe resources for ProSe operation from the new cellif it supports ProSe operation. After acquiring new set of ProSeresources the UE may start using the ProSe resources for ProSe operationon the sidelink of the carrier for which the resources are assigned.

Where:

Tmax_total is function of Tmax1, Tmax2 and Tmax 3. Examples of functionare maximum, minimum, average etc. As an example:

-   Tmax_total=MAX (Tmax1, Tmax2, Tmax3)

Where:

-   Tmax1 is the duration over which the UE has not identified any cell    on the intra-frequency carrier since in ONC (and/or a pre-defined    time T2 after T1, the beginning of ONC) and beyond Tmax1 the UE can    identify an intra-frequency cell during the second time period (e.g.    over intra-frequency cell identification time). Example of Tmax1=6    seconds.-   Tmax2 is the duration over which the UE has not identified any cell    on the inter-frequency carrier since in ONC and beyond Tmax2 the UE    can identify an inter-frequency cell during the second time period    (e.g. over inter-frequency cell identification time). Example of    Tmax2=5 seconds.-   Tmax3 is the duration over which the UE has not identified any cell    on the inter-frequency carrier since in ONC and beyond Tmax3 the UE    can identify an inter-RAT cell during the second time period (e.g.    over inter-frequency cell identification time). Example of Tmax3=4    seconds.

UE implementation aspects for cell search in ONC are discussed in thefollowing.

Exemplary cell detection when out-of-WAN coverage is illustrated inFIGS. 3 and 4 and is further described below.

When it is time to carry out cell detection on a carrier frequency f(100), the UE first checks whether the modem still is synchronized tothe network (105; Details in 220-235). In case network coverage was lostrecently, e.g. within 15-30 s, the oscillator (XO, VCXO, TCXO) may stillgive sufficiently accurate frequency reference for cell detection to becarried out. If this is the case (105; YES) a regular cell detection iscarried out, without taking oscillator drift into account (165).Concretely it is assumed that the absolute frequency offset is withinthe capture range for frequency offset estimation and hence in the range±2 kHz.

In case it is assessed that the oscillator drift is too large for it tobe used for cell detection (105; NO), the UE may check if an externalfrequency reference is available, for instance from a companion GPScircuit which may be active and has locked on satellites. If suchfrequency source is available (110; YES) the UE tunes the modemoscillator using the external reference (125), sets the oscillatorstatus to Tuned to WAN (140; Details in 200-210), and then carries out aregular cell detection (165).

In case no external frequency reference is available (110; NO) the UEchecks whether it is in the coverage of any unacceptable cell (e.g. ofanother operators network, or a cell that it for other reasons is notallowed to use). If so (115; YES) the UE tunes in to the carrier of theunacceptable cell to acquires synchronization (130). It then sets theoscillator status to Tuned to WAN (140; Details in 200-205), and carriesout a regular cell detection (165).

In case no unacceptable cells have been encountered in previous searchessince the UE went out of WAN coverage (115; NO), the UE checks whetherit has connection to the WAN via a peer device (i.e. operating in D2D,ProSe). If so (120; YES), depending on the maximum number of devicesthat can form a link between the UE and WAN (which may be assumed,specified in standards, or signaled), the UE will have to account for alarger frequency tolerance, X ppm, than had it been directly connectedto the network. The reason is that each link between the UE and the WANadds to the tolerance hence the frequency experienced by a UE whenreceiving a signal from a peer device may have a larger tolerance to thenominal frequency than the allowed base station tolerance (i.e., ±0.01ppm for LTE macro cell; 3GPP TS 36.101). The UE thus runs cell detectionwhere it accounts for the potentially large frequency offset (145).Particularly, in case the absolute frequency offset can be assumed to beoutside the range ±2 kHz, disambiguation of the frequency offsetestimate may be needed, as outlined in U.S. Pat. No. 8,675,788“Correction of frequency offsets greater than the Nyquist frequency”.Moreover, if the maximum absolute frequency offset can exceed 3.75 kHzthe UE may need to carry out a search over a frequency grid, as outlinedin U.S. Pat. No. 8,447,005 “Frequency synchronization methods andapparatus”, where the width of the search depends on carrier frequency fand tolerance X.

In case the UE does not have any established connection with a peerdevice (120; NO), in a first alternative (Alt.1) it runs cell detectionassuming the maximum initial frequency tolerance as specified for themodem (150). This tolerance may be as high as 15-20 ppm due toimperfections, ambient temperature, and aging. One cell detectionapproach for this case is outlined in U.S. Pat. No. 8,447,005 “Frequencysynchronization methods and apparatus”.

In another alternative (Alt.2) the UE may assess the worst case driftand a corresponding tolerance Y since last synchronization to the WAN(135; Details in 240-260). It then runs cell detection where it takesthe tolerance Y into account (155)—similar to step (145) above.

When cell detection has been carried out, if a cell was detected oncarrier frequency f (175; YES), the oscillator status is set to Tuned toWAN (160; Details in 200-205) and information about the cell is storedfor later use (170; YES), e.g. SI acquisition and random access.

The oscillator's tuning status may be tracked e.g. by logging the timeat which the last AFC correction was made while the UE was receivingsuccessfully from the WAN (e.g. indicated by successful CRC check) (200,205).

In its simplest form, the UE may assess the status of the oscillator bycalculating how much time has elapsed since the last tuning (225). Ifthe elapsed time is less than some Tmax (225; NO), the oscillator isconsidered to be untuned with respect to the WAN (235); otherwise it isassumed to be tuned (230). Tmax may be a conservative value for whichthe drift of the oscillator remains within an acceptable toleranceregardless of what activity level the UE had before going out of WANcoverage.

Several factors are impacting the oscillator drift, with aging andtemperature changes as the dominating contributors. Aging can bediscarded if only considering the drift that happens during the timesince the last synchronization to WAN. Temperature changes depend onwhat activity the UE was involved in immediately before going out-of-WANcoverage and the activity after going out-of-WAN coverage. The UE canpredict the maximum tolerance by taking the time since the lastsynchronization (245) and activities before and after goingout-of-coverage (e.g. data call before and cell search after) as a proxyfor the temperature change (250), and/or the actual temperaturetrajectory close to the crystal (when such measurements are supported).This information can be used for estimating the worst case tolerance atcurrent time (260), thereby potentially reducing the number of frequencyoffset grid points when carrying out cell detection.

A method in a network node configuring a D2D enabled UE with carriersfor cell detection in out of network coverage is discussed in thefollowing.

In this variant the network node (e.g. providing the old serving cell ofthe D2D enabled UE) configures the D2D enabled UE with informationrelated to detecting cells on serving carriers, configuredinter-frequency and configured inter-frequency carriers when the D2Denabled UE would go into ONC. The network node may be configuredaccordingly and/or comprise a configuring module for such configuring.

The information may comprise of an indicator that the D2D enabled UEshould detect cells on all carriers during the first phase i.e. servingcarriers, configured inter-frequency and configured inter-frequencycarriers in ONC. The information may also comprise of an indication thatonly a subset of serving carriers, configured inter-frequency andconfigured inter-frequency carriers should be used for detecting cellsin ONC. In this case the information about the subset of carriers mayalso be provided to the UE. The information may also comprise of anindicator that only carriers or subset of carriers configured formeasurements in a particular RRC state may be used for detecting cellsin ONC e.g. those configured in RRC connected state. The information mayalso comprise of an indicator that all carriers or subset of carriersconfigured for measurements in all RRC states may be used for detectingcells in ONC e.g. those configured in RRC idle and RRC connected states.

The information may also comprise of list of frequency bands and/orcarriers within certain bands on which the UE should detect cells in ONCif no cell is detected within the first phase e.g. carriers/bands onwhich to detect cells during the second phase of cell detection. Theinformation may also comprise of RATs whose cells are to be searched bythe UE during the second phase. The information may also comprise oforder with which the UE should search cells on different RATs UE duringthe second phase.

Prior to configuring the UE with one or more set of the aboveinformation, the network node may determine (and/or the network node maybe adapted accordingly and/or comprise a determining module for suchdetermining) the information based on one or more of the followingcriteria or pre-defined knowledge:

-   -   Frequency bands used in a coverage area where UE may operate        while in OCN;    -   Carrier frequencies within the identified bands used in a        coverage area where UE may operate while in OCN;    -   RATs (e.g. LTE TDD, LTE FDD, UMTS, GSM etc) within the        identified bands used in a coverage area where UE may operate        while in OCN;    -   Capability of the UE in terms of supported bands;    -   Capability of the UE in terms of supported RATs on different        bands supported by the UE.

For example the network node may configure the UE only those bands andRATs for cell search in the first and the second phases, which areavailable in the coverage area as well supported by the UE.

The network node can acquire information about the capability of the UEin terms of supported bands, RATs etc based on indication received fromthe UE.

According to the solution, the measurement configuration configured bythe last PCell may be valid up to a certain time at the UE. This timemay be different for different type of cell search configurations. Bytaking this time and measurement configuration configured by the lastPCell into account at a ProSe UE which has been out of network coverage,the cell search procedure can be performed much faster. The celldetection for which the UE has prior-knowledge (e.g. measurementconfigurations) may be prioritized over others. In addition, theinterference caused by the ProSe UE due to the pre-configured ProSeresources which the ProSe UE uses while operating in out of networkcoverage may be reduced. If the ProSe UE has been out of networkcoverage for long time (e.g. duration beyond a threshold) that the oldmeasurement configurations are invalid or unreliable, then the UE mayperform initial cell search procedure on all carriers of subset or allits supported bands.

There is generally described a UE adapted to carry out any of themethods for operating a UE described herein, in particular any of themethod for cell search performed by a UE described herein. The UEgenerally may comprise a cell search module for performing cell searchas described herein. It may be considered that the UE comprise aconfiguration checking module for checking a configuration ofpre-determined times (e.g. T2 and/or T3, and/or any one or any onecombination of Tmax(1,2,3,total) described herein).

Performing cell search may be performed based on the checking. Checkingmay include whether at a given time, a cell search according to adefined phase has provided a cell search identification, and/or whichcell search operations (e.g. on which carriers) are to be performed at agiven time, e.g. depending on pre-defined time thresholds and/or aremembered and/or stored configuration. There are also disclosed acorresponding program product and a corresponding storage medium.

Independently or in addition, there is described a method for operatinga D2D enabled UE for a cellular communication network, comprisingperforming a cell search, which may be performed in an out of coverage(OOC or ONC) condition of the UE and/or after determining and/ordetecting such a condition. There may be considered a user equipmentadapted for such performing and/or comprising a cell search module forsuch performing. Performing a cell search may be based on a firstmeasurement configuration during a first phase. Performing a cell searchmay be based on a second measurement configuration during a secondphase, wherein the second phase may be different from the first phase,in particular longer than the first phase and/or, the second phase maybegin when the first phase ends; and/or time thresholds defining thefirst phase and the second phase may be chosen and/or determined and/orconfigured accordingly.

Optionally, performing a cell search may be based additionally on athird measurement configuration during a third phase, wherein the thirdphase may be different from the first phase and/or the second phase, inparticular longer than the first phase and/or the second phase, and/orthe third phase may begin when the first phase and/or the second phaseends; and/or time thresholds defining the third phase, the first phaseand the second phase may be chosen and/or determined and/or configuredaccordingly.

Performing a cell search may be interrupted during any of the phase/s ifa cell has been identified using the measurement configurationassociated to the respective phase. The method may comprise detecting anout of coverage condition, e.g. before performing the cell search. Theuser equipment may be adapted for such detecting and/or comprise adetecting module for such detecting. The method may comprise configuringthe UE for the first measurement configuration based on allocationand/or configuration data received from a network and/or network node.The UE may be adapted for such configuring and/or for receiving suchdata, and/or may comprise a configuring module for such configuringand/or a receiving module for such receiving. The method and/or UE mayin particular comprise any of the features of a method for operating aUE described herein and/or be adapted correspondingly.

There is also described a method for operating a network node,comprising configuring a D2D enabled UE with a first measurementconfiguration. There may be considered a network node adapted for suchconfiguring and/or comprising a configuring module for such configuring.The method may comprise determining the first measurement configurationand/or a first time phase and/or a first time threshold, e.g. based onoperating conditions.

The network node may be adapted for such determining and/or comprise aconfiguration determining module for such configuring. Configuring maycomprise configuring the UE with a second measurement configurationand/or a second time phase and/or a second time threshold. Configuringmay comprise configuring the UE with a third measurement configurationand/or a third time phase and/or a third time threshold. Configuring theUE may comprise transmitting allocation data and/or configuration datarepresenting the first measurement configuration and/or the secondmeasurement configuration and/or the third measurement configurationand/or the associated time phase/s and/or thresholds to the UE. Thesecond phase may be different than the first phase, in particular longerthan the first phase and/or the second phase may begin when the firstphase ends and/or the time thresholds may be chosen and/or determinedand/or configured accordingly.

The third phase may be different from the first phase and/or the secondphase, in particular longer than the first phase and/or the secondphase, and/or the third phase may begin when the first phase and/or thesecond phase ends; and/or time thresholds defining the third phase, thefirst phase and the second phase may be chosen and/or determined and/orconfigured accordingly.

The first measurement configuration and/or the second measurementconfiguration may, independently or in addition to any of the otherfeatures disclosed therein, in particular be defined as outlined in E1to E6, corresponding to different types of cells.

Some embodiments described are:

E1. A method in a ProSe capable UE configured with a first ProSeconfiguration for a ProSE operation on first a side link and operatingin out of network coverage (ONC), the method comprises:

-   -   Attempting to detect at least one first type of cell operating        on a first type of carrier configured with a first measurement        configuration during a first maximum time period, Δτ₁;    -   Where Δτ₁=T2−T1, is the duration over which the UE is able to        use the first measurement configuration for detecting the first        cell;    -   T1 is a time instance when the UE moves into ONC.    -   Attempting to detect at least one second type of cell operating        on a second type of carrier configured with a second measurement        configuration, provided that none of the first type of cell is        detected within a third maximum time period, Δτ₃;    -   Where Δτ₃=Δτ₁+Δτ₂; and is Δτ₂ a second maximum time period over        which the UE can identify the first cell.    -   Adapting one or more ProSe operations based on the detection of        the at least one first type of cell or the second type of cell.

E2 (Independent or according to E1) A method in a ProSe capable UEconfigured with a first ProSe configuration for a ProSE operation onfirst a side link and operating in out of network coverage (ONC), themethod comprises:

-   -   Attempting to detect at least one first type of cell operating        on a first type of carrier configured with a first measurement        configuration starting from time T1 which is a time instance        when the UE moves into ONC.    -   Attempting to detect at least one second type of cell operating        on a second type of carrier configured with a second measurement        configuration, provided that none of the first type of cell is        detected within a maximum time period, Δτ′;

-   Where Δτ′ and is the time period over which the UE has not    identified any first type of the cell on the first type of carrier    since entering in ONC and beyond which the UE can identify the first    type of cell during a second time period (e.g. over cell    identification time of the first type of cell).    -   Adapting one or more ProSe operations based on the detection of        the at least one first type of cell or the second type of cell.

E3. The method of E1 or E2, wherein the first type of cell may belongingto any one or any combination of:

an intra-frequency or serving carrier used by the UE before entering inthe ONC;

-   -   a carrier frequency whose sidelink is preconfigured with ProSe        resources for ProSe operation of the UE in ONC;    -   a carrier frequency of the side link or a carrier frequency        associated with the carrier frequency of the first side link;    -   an inter-frequency carrier configured by the last serving cell        for one or more inter-frequency measurements;    -   an inter-RAT carrier configured by the last serving cell for one        or more inter-RAT measurements. This definition of the first        type is applicable for any embodiment or variant, e.g. any        method for operating a UE, described in this specification.

E4. The method of one of E1 to E3, wherein the second type of cell maybelonging to any of:

-   -   an inter-frequency carrier belonging to any of a frequency band        supported by the UE, regardless of whether said carrier is        configured or not for the inter-frequency measurement;    -   an inter-RAT carrier belonging to any of a frequency band        supported by the UE, regardless of whether said carrier is        configured or not for the inter-RAT measurement. This definition        of the second type is applicable for any embodiment or variant,        e.g. any method for operating a UE, described in this        specification.

E5. The method of one of E1 to E4, wherein the first measurementconfiguration comprises:

-   -   Information about at least one intra-frequency carrier and may        further comprise of one or more non-carrier carriers, said        information is received from the last serving cell;    -   Timing information about one or more or more cells operating on        one or more second type of carriers. This definition of the        first measurement configuration is applicable for any embodiment        or variant, e.g. any method for operating a UE, described in        this specification.

E6. The method of one of E1 to E5, wherein the second measurementconfiguration comprises:

-   -   Information about carriers of at least one frequency band        supported by the UE, said information is retrieved from        pre-defined or stored information. This definition of the second        measurement configuration is applicable for any embodiment or        variant, e.g. any method for operating a UE, described in this        specification.

E7. The method of one of E1 to E6, wherein adapting the ProSe operationcomprises:

-   -   Stopping the ProSe operation on the first side link if at least        one cell belonging to the first or the second types of cells is        detected by the UE

E8. The method of any one of E1 to E7, wherein adapting the ProSeoperation, further comprises:

-   -   Receiving a second ProSe configuration for the ProSe operation        on a second side link from the detected cell; and    -   Performing ProSe operation using the second ProSe configuration        on the second side link or not performing any ProSe operation if        no second ProSe configuration is received from the detected        cell.

E9. The method of one of E1 to E8, wherein the cell of the first celltype can be detected within Δτ₃=Δτ₁ i.e. Δτ₂=0.

E10. The method of one of E1 to E9, wherein Δτ₁=MAX (X, Y, Z), where X,Y and Z are time periods over which the first measurement configurationcan be used for detecting cells on intra-frequency carrier(s) usedbefore entering ONC, configured inter-frequency carrier(s) andconfigured inter-RAT carrier(s) for measurements by the last servingcell respectively.

E11. The method of one of E1 to E10, wherein Δτ₂=MAX (X′, Y′, Z′), whereX′, Y′ and Z′ are time periods over which the UE can detect cell onintra-frequency carrier(s) used before entering ONC, on configuredinter-frequency carrier(s) and on configured inter-RAT carrier (s) formeasurements by the last serving cell respectively.

E12. The method of one of E1 to E11, wherein Δτ₂=MAX(X′, Y′ *N_(freq),Z′ *N_(freq)), where N_(freq) is the configured number ofinter-frequency carrier(s) and inter-RAT carrier(s) for measurements bythe last serving cell respectively.

N1. A method in a network node serving a ProSe capable UE configuredwith a first ProSe configuration for a ProSE operation on first a sidelink, the method comprises:

-   -   Determining a first measurement configuration to be used by the        UE for detecting at least one first type of cell operating on a        first type of carrier and operating in out of network coverage        (ONC) during a first maximum time period, Δτ₁;    -   Where Δτ₁=T2−T1, is the duration over which the UE is able to        use the first measurement configuration for detecting the first        cell;    -   T1 is a time instance when the UE moves into ONC.    -   Determining a second measurement configuration to be used by the        UE for detecting at least one second type of cell operating on a        second type of carrier, provided that none of the first type of        cell is detected within a third maximum time period, Δτ₃;    -   Where Δτ₃=Δτ₁+Δτ₂; and is Δτ₂ a second maximum time period over        which the UE can identify the first cell.    -   Transmitting the determined first measurement configuration and        the second measurement configuration to the UE.

N2 The method of N1, where the first and/or the second measurementconfigurations are determined based on one or more of the followingcriteria:

-   -   Frequency bands used in a coverage area where UE may operate        while in OCN;    -   Carrier frequencies within the identified bands used in a        coverage area where UE may operate while in OCN;    -   RATs (e.g. LTE TDD, LTE FDD, UMTS, GSM etc) within the        identified bands used in a coverage area where UE may operate        while in OCN;    -   Capability of the UE in terms of supported bands;    -   Capability of the UE in terms of supported RATs on different        bands supported by the UE.

Alternatively or additionally, there is disclosed for consideration thefollowing suggested clause, which is a suggested amendment to 3GPPTS36.133 V12.6.0 and has to be read in the context thereof.

Cell Identification Requirements for ProSe UE in Any Cell SelectionState

11.3.1 Introduction

This clause contains requirements on the UE capable of ProSe directcommunication regarding cell detection in any cell selection state.

The UE can be preconfigured with ProSe resources for ProSe operation inany cell selection state.

The requirements in this section are applicable for the ProSe in anycell selection state. The ProSe UE in any cell selection state (and/orin a ONC condition, which may be a condition of cell selection state)shall continuously search (e.g., according to the above and/orcorresponding measurement configurations) for any detectable cellbelonging to:

-   the last intra-frequency carrier,-   the carrier frequency preconfigured with ProSe resources for ProSe    operation in any cell selection state,-   the carrier frequencies configured for inter-frequency and/or    inter-RAT measurements by the last PCell and-   the carriers not configured by the last PCell but belong to the    frequency bands supported by the UE.

11.3.2 Cell Identification Requirements

11.3.2.1 Identification of Cells on Intra-Frequency Carrier or CarrierPreconfigured with ProSe Resources

The UE capable of ProSe direct communication immediately upon enteringin any cell selection state shall search for any detectable cell onintra-frequency carrier belonging to the last PCell or the carrierpreconfigured with ProSe resources, e.g. according to a firstmeasurement configuration and/or during a first phase.

An intra-frequency cell or a cell on the carrier preconfigured withProSe resources is considered detectable provided it meets theintra-frequency cell identification conditions specified in section8.1.2.2.

If the following condition is met then the UE shall be capable ofidentifying a detectable cell on the last intra-frequency carrier or onthe carrier preconfigured with ProSe resources within 2*T_(Measurement)_(_) _(Period, Intra), which is defined in clause 8.1.2.2:

-   The ProSe UE has been in any cell selection state within a time    period, T1, where T1≦[5] seconds.

Otherwise the UE shall be capable of identifying a detectable cell onthe last intra-frequency carrier or on the carrier preconfigured withProSe resources within 2*T_(identify) _(_) _(intra), which is defined inclause 8.1.2.2.

11.3.2.2 Identification of Cells on Inter-Frequency Carriers

The UE capable of ProSe direct communication immediately upon enteringin any cell selection state shall search for any detectable cell oninter-frequency carriers configured for measurements by the last PCell(e.g., according to a second measurement configuration and/or to asecond phase).

An inter-frequency cell is considered detectable provided it meets theinter-frequency cell identification conditions specified in section8.1.2.3.

If the following condition is met then the UE shall be capable ofidentifying a detectable cell on any of the last configuredinter-frequency carrier within T_(Measurement) _(_) _(Period, Inter)corresponding to gap id #0 as defined in clause 8.1.2.3:

-   The ProSe UE has been in any cell selection state within a time    period, T2, where T2≦[5] seconds.

Otherwise the UE shall be capable of identifying a detectable cell onany of the last configured inter-frequency carrier within T_(identify)_(_) _(inter) corresponding to gap id #0 as defined in clause 8.1.2.3.

11.3.2.3 Identification of Cells on Inter-RAT Carriers

The UE capable of ProSe direct communication immediately upon enteringin any cell selection state shall search for any detectable cell oninter-RAT carriers configured for measurements by the last PCell (e.g.according to a third measurement configuration and/or a third phase).

An inter-RAT cell is considered detectable provided it meets theinter-RAT cell identification conditions for the relevant RAT asspecified in section 8.1.2.4.

If the following condition is met then the UE shall be capable ofidentifying a detectable cell on any of the last configured inter-RATcarrier within T_(Measurement) _(_) _(RAT) corresponding to gap id #0:

-   The ProSe UE has been in any cell selection state within a time    period, T3, where T3≦[5] seconds.

Otherwise the UE shall be capable of identifying a detectable cell onany of the last configured inter-RAT carrier within T_(identify, RAT)corresponding to gap id #0. Where, T_(Measurement RAT) andT_(identify, RAT) are the measurement period and cell identificationtime respectively for the relevent RAT as defined in clause 8.1.2.4.

11.3.2.4 Identification of Cells on Non-Configured Carriers

The UE capable of ProSe direct communication shall also search for anydetectable cell on carriers, which are not configured by the last PCellbut belong to the frequency bands supported by the UE provided thefollowing condition is met:

-   The UE has not identified any cell on any of the last    intra-frequency carrier, the carrier preconfigured with ProSe    resources, the configured inter-frequency carriers and the    configured inter-RAT carriers within the duration of MAX (T1, T2,    T3).

11.3.3 ProSe UE Procedure Upon the Cell Identification

If the UE has identified any cell on any of the intra-frequency carrier,the carrier preconfigured with ProSe resources, the configuredinter-frequency carriers, the configured inter-RAT carriers and thenon-configured carriers belonging to the supported bands then:

-   the UE shall stop using the preconfigured resources for ProSe    operation by the last PCell and-   the UE may use resources assigned by the newly identified cell for    ProSe operation on the slidelink on the carrier of the newly    identified cell.

The UE and/or the network node may be adapted accordingly.

Alternatively or additionally, there is disclosed for consideration:

1. ProSe UE in Out-of-Coverage

A ProSe UE which is out-of-coverage is required to scan for new cellularcells that it can connect to. The ProSe UE can be out-of-coverage fordifferent periods, and the length of this period affects the total cellsearch delay. For example, if the ProSe UE has been out-of-coverage forvery short time and it detects a cellular cell, then some of the oldconfigurations may still be valid, e.g. frequency- and timesynchronization.

On the contrary, if the ProSe UE has been out-of-coverage for long time,the frequency- and time synchronization may have changed or the oldconfigurations may not be valid any longer. This may lead to longer cellsearch time. There should be a time, Δ, up to which the ProSe UEremembers its old receiver configuration.

Examples of such configurations (in particular corresponding to ameasurement configuration, which may be a first measurementconfiguration) are:

-   Time and frequency configuration-   Intra-band center-frequency location-   Supported band configuration

Remembering these receiver configurations will lead to reduced cellsearch time up to a certain time. This may correspond to a neighbourcell search procedure and it may be possible to reuse some of theexisting cell search requirements in this case.

The second case is when the UE has been out-of-coverage for long time,e.g. more than X seconds that the UE has lost its old receiverconfiguration. This may correspond to an initial cell search procedurewhich will take even longer time, e.g. few seconds or minutes in theworst case.

Examples of pre-configured parameters that are configured forout-of-coverage scenarios are:

-   P-Max-ProSe; parameter used to limit the maximum transmit power when    the

ProSe UE operates in out-of-coverage.

-   additionalSpectrumEmissions-ProSe; parameter used to adjust the    transmission to meet the region-specific regulatory emission    requirements when ProSe UE operates in out-of-coverage.

The problem may arise due to the pre-configured ProSe resources when itis in the vicinity of a new cellular cell or when it detects a new cellon the cellular carrier. This is explained below.

When the ProSe UE is camped on a cell or it has a serving cell (PCell),then the ProSe UE should use the radio resources indicated by its PCell.These are indicated by the eNB using the SIB or dedicated signaling. IfProSe UE continues to use the pre-configured radio resources which werederived particularly for the out-of-coverage scenario in in-coveragescenario, this may result in that the ProSe harming the cellularnetwork. Therefore there is a need for UE requirements to ensure that inout of network coverage the UE uses ProSe only where it is allowed to doso.

The newly detected cell by ProSe may be of following types:

-   intra-frequency cells (same carrier as that of the last serving    cell)-   cells on a carrier preconfigured with ProSe resources for ProSe    operation in out of network coverage. This carrier can be the same    or different than the last intra-frequency carrier.-   inter-frequency cells-   inter-RAT cells

FIG. 1 shows a ProSe UE which has lost coverage to old cell, while beingout of network coverage performing ProSe Communication with anotherProSe UE using the pre-configured ProSe resources.

2. Cell Detection Requirements for ProSe UE in Out-of Coverage

In this section the time required for the ProSe UE in out-of-coverage todetect a cell on intra-frequency, configured inter-frequency orconfigured inter-RAT carriers or any non-configured carrier isdiscussed.

2.1 Detection of intra-frequency cells or cells on preconfigured ProSecarrier by ProSe UE in out-of coverage

In this section it is assumed that the newly detected cell is anintra-frequency cell on the last intra-frequency carrier before enteringONC or the detected cell may belong to the carrier preconfigured withProSe resources for ProSe operation in out of network coverage. Thepreconfigured ProSE carrier can be the same or different than the lastintra-frequency carrier.

The detected cell can be the same old serving cell ProSe UE wasconnected to earlier or it can also be a new cell on any of the twocarriers. In order to detect the new cell, the UE receiver has to firstfind the location of center frequency and then detect the PSS/SSS in 6RBs located in the center frequency. For intra-frequency cells thecenter-frequency is located in the same position regardless of the band.Thus the new cell is detected quicker provided that the old measurementconfiguration is kept within the UE at this point in time, i.e. the oldreceiver configurations are still applicable. If this is the case, inour view the existing cell identification requirement can be reused forProSe UE.

FIG. 2 illustrates the events in a time-axis of a ProSe UE in an examplescenario. At time T1, the UE loses its connection to PCell, i.e. it goesout of network coverage. T2 is the point in time when the UE loses itsold receiver configuration or at which the old receiver configurationsbecome invalid. If the UE has been out-of-coverage for long time, e.g.time greater than Δ1, that the old measurement configuration is notvalid or lost, then the cell search procedure may take longer time andit may correspond to initial cell search procedure.

This scenario can be compared to a HO (handover) scenario wherein the UEloses its connection to the old PCell for a short time. It this clause,a cell which has been unknown requires time to perform cell search.However, if the cell has been known for the last 5 seconds, then thecell may still be known at the UE since the center frequency is known.In this case the UE does only have to perform a measurement. In additionto the intra-frequency cell search, if the UE has to perform search oncarrier preconfigured with ProSe resources the total cell time needs tobe scaled up by multiplying the intra-frequency cell search time with afactor of 2. This is because the UE will have to share its cell searchresources for detecting the cell on up to two carriers in parallel. Incase the preconfigured ProSe carrier is the same as the lastintra-frequency carrier then the UE can detect the new cell over shorttime. But it is suggested to define one set of requirements applicableto both cases i.e. use scaling factor of 2.

An intra-frequency cell or a cell on the carrier preconfigured withProSe resources is considered detectable provided it meets theintra-frequency cell identification conditions specified according tothe standard.

-   Proposal #1: The ProSe UE in out-of-coverage shall continuously    search for any detectable cell on the last intra-frequency carrier.

Proposal #2: A ProSe UE which has been out-of-coverage for a time lessthan Δ1, where Δ1≦[5] s shall be capable of identifying a detectablecell on the last intra-frequency carrier or on the carrier preconfiguredwith ProSe resources within 2*T_(Measurement) _(_) _(Period, Intra)which is defined in clause 8.1.2.2.

Proposal #3: If the ProSe UE has been out-of-coverage for a time greaterthan Δ1, where Δ1>[5] s, then the UE shall be capable of identifying adetectable cell on the last intra-frequency carrier on the carrierpreconfigured with ProSe resources within 2*T_(identify) _(_) _(intra).

Regardless of what cell on intra-frequency or preconfigured ProSecarrier is detected, the ProSe UE shall stop using the pre-configuredProSe resources as it detects a new cellular cell. ProSe UE shallinstead use the assigned radio resources by the new cell if it supportsProSe else it shall not use ProSe if ProSe is not supported in the newcell.

2.2 Detection of Inter-Frequency Cells by ProSe UE in Out-of Coverage

If the ProSe UE was configured with inter-frequency carriers formeasurements by the old PCell then in out of coverage the UE should alsocontinue searching inter-frequency cells on the previously configuredinter-frequency carriers.

Similar to the discussion in previous section, if the ProSe UE has someprior knowledge about e.g. supported bands, center-frequency locationetc. the new inter-frequency cell can be detected much faster. The UEmay be able to keep some prior knowledge up to certain time, e.g. up totime T2 in FIG. 2.

In this case, the procedure becomes similar to neighbour cell search andthen the existing requirement for inter-frequency cell search can bereused [36.133]. The difference, however, is that the UE performsneighbour cell search on inter-frequency cells using measurement gaps.Typically, measurement gaps of 6 ms every 40 ms are used forinter-frequency cell detection. It is notable that a ProSe UE which isalready in out-of-coverage may be able to detect the new cell evenquicker since it does not require any measurement gaps, i.e. it cansearch any time.

An inter-frequency cell is considered detectable provided it meets theinter-frequency cell identification conditions specified according tothe standard.

Proposal #4: The ProSe UE in out-of-coverage shall continuously searchfor any detectable cell on inter-frequency carriers configured by thelast PCell.

Proposal #5: A ProSe UE which has been out-of-coverage for a time lessthan Δ1, where Δ1≦[5] s shall be capable of identifying a detectablecell on the last configured inter-frequency carrier corresponding to gapid #0 within as T_(Measurement) _(_) _(Period, Inter) which is definedin clause 8.1.2.3.

Proposal #6: If the ProSe UE has been out-of-coverage for a time greaterthan Δ1, where Δ1>[5] s, then the UE shall be capable of identifying adetectable cell on the last configured inter-frequency carrier withinT_(identify) _(_) _(inter) corresponding to gap id #0 as defined in thestandard.

Whenever inter-frequency is detected, the ProSe UE shall stop using thepre-configured ProSe resources as it detects a new cellular cell on anyinter-frequency carrier. ProSe UE shall instead use the assigned radioresources by the new cell if it supports ProSe else it shall not useProSe if ProSe is not supported in the new cell.

3.3 Detection of Inter-RAT Cells by ProSe UE in Out-of Coverage

If the ProSE UE was configured with inter-RAT carriers for measurementsby the old PCell then in out of coverage the UE should also continuesearching inter-RAT cells on the previously configured inter-RATcarriers.

In this case the detected cell belongs to different RAT. Existinginter-RAT cell detection requirements defined in the standard (Inter RATmeasurements) [TS 36.133] can also be reused provided that the UE hasbeen in out of coverage for not more than Δ3. The neighbour cell searchon inter-RAT cells is performed using measurement gaps. Typically,measurement gaps of 6 ms every 40 ms are used for inter-frequency celldetection.

An inter-RAT cell is considered detectable provided it meets theinter-RAT cell identification conditions for the relevant RAT asspecified in the standard.

Assuming that a ProSe UE has been out of network coverage during timeΔ1, where Δ1<=[5] s, then the ProSe UE is able to detect inter-RAT cellon any of the configured inter-RAT carriers within the inter-RAT celldetection time defined for measurement gaps configuration #0 in section8.1.2.3 (E-UTRAN inter frequency measurements) in [36.133].

Proposal #7: A ProSe UE which has been out-of-coverage for a time lessthan Δ1, where Δ1≦[5] s shall be capable of identifying a detectablecell on any of the last configured inter-RAT carrier corresponding togap id #0 within T_(Measurement) _(_) _(Period, RAT) which as defined inthe standard.

Proposal #8: If the ProSe UE has been out-of-coverage for a time greaterthan Δ1, where Δ1>[5] s, then the UE shall be capable of identifying adetectable cell on any of the last configured inter-RAT carrier withinT_(identify) _(_) _(RAT) corresponding to gap id #0 as defined in thestandard.

Whenever inter-RAT is detected, the ProSe UE shall stop using thepre-configured ProSe resources as it detects a new cellular cell on anyinter-RAT carrier. ProSe UE shall instead use the assigned radioresources by the new cell if it supports ProSe else it shall not useProSe if ProSe is not supported in the new cell.

3.4 Detection of Cells by ProSe UE in Out-of Coverage after MeasurementConfiguration Expires

This section pertains to a ProSe UE performing cell search on allsupported carriers by the UE, i.e. not only the carriers which wereconfigured for measurements by the last PCell. In this case, the ProSEUE has to search for cells on all supported frequency bands i.e. withineach band it will search cells. For example in LTE the UE may have todetect PSS/SSS in every 100 KHz (channel raster). If PSS/SSS is detectedthen it knows where the center frequency is because PSS/SSS aretransmitted in the center frequency and it will align its frequency- andtime-synchronization towards that new cell. This corresponds to theinitial cell search procedure and therefore requires no requirements.

Proposal #9: The ProSe UE in out of coverage shall search for anydetectable cells on all supported carriers by the UE. However in thiscase no cell search requirements are specified.

If any cell is detected as part of the initial cell search then theProSe UE shall stop using the pre-configured ProSe resources. The ProSeUE shall instead use the assigned radio resources by the new cell if itsupports ProSe otherwise it shall not use ProSe if ProSe is notsupported in the new cell.

3.5 Overall Requirements for Cell Detection by ProSe UE in Out-ofCoverage

As stated above that it is important that the pre-configured ProSeresources are only used when the UE is out of network coverage. But assoon as the ProSe UE detect any cell while being in out of networkcoverage, the ProSe UE should stop using the pre-configured resources inorder to not harm or to reduce its negative impact on the that new cell.Therefore it is necessary that any new detectable cell is identified bythe UE as quickly as possible.

The overall ProSe UE procedure for detecting a cell and stopping the useof pre-configured resources for ProSe operation when the ProSe UE is inout of network coverage is as follows:

-   The ProSe UE upon entering in out of network coverage at time T1    shall continuously detect cells belonging to:-   the intra-frequency of the last PCell or on the carrier    preconfigured with ProSe resources,-   the inter-frequency carriers configured for measurements by the last    PCell for gap Id #0 defined in the standard,-   the inter-RAT carriers configured for measurements by the last PCell    for gap Id #0 defined in the standard.-   If the UE is unable to detect any cell on the intra-frequency or    carrier configured with ProSe resources, the configured    inter-frequency or the configured inter-RAT carriers by the last    PCell, then the UE shall also continuously detect cells on carriers    of all frequency bands supported by the UE.-   If the UE is able to detect any cell on the intra-frequency- or    ProSe configured carrier, the configured inter-frequency or the    configured inter-RAT carriers or on any other carrier, then the UE    shall stop using resources for ProSe pre-configured by the last    PCell.-   If the newly detected cell supports ProSe then the UE may use radio    resources assigned by the new cell for ProSe operation.

Cell detection of ProSe UEs in out of network coverage scenario has beendiscussed in the context of the current LTE standard. There are proposedProSe UE procedures for pre-configured ProSe resources upon cellidentification and requirements on time for cell detection that maybelong to the intra-frequency- or ProSe configured carrier, theconfigured inter-frequency or the configured inter-RAT carriers or onany other carrier. A main objective of this discussion can be summarizedas follows:

The ProSe UE upon entering in out of network coverage at time T1 shallcontinuously detect cells belonging to:

-   -   the intra-frequency of the last PCell or on the carrier        preconfigured with ProSe resources,    -   the inter-frequency carriers configured for measurements by the        last PCell for gap Id #0 defined in the standard,    -   the inter-RAT carriers configured for measurements by the last        PCell for gap Id #0 defined in the standard.

If the UE is unable to detect any cell on the intra-frequency or carrierconfigured with

ProSe resources, the configured inter-frequency or the configuredinter-RAT carriers by the last PCell, then the UE shall alsocontinuously detect cells on carriers of all frequency bands supportedby the UE.

If the UE is able to detect any cell on the intra-frequency- or ProSeconfigured carrier, the configured inter-frequency or the configuredinter-RAT carriers or on any other carrier, then the UE shall stop usingresources for ProSe pre-configured by the last PCell.

If the newly detected cell supports ProSe then the UE may use radioresources assigned by the new cell for ProSe operation.

Some useful abbreviations are:

In the context of this description, wireless communication may becommunication, in particular transmission and/or reception of data, viaelectromagnetic waves and/or an air interface, in particular radiowaves, e.g. in a wireless communication network and/or utilizing a radioaccess technology (RAT). The communication may involve one or more thanone terminal connected to a wireless communication network and/or morethan one node of a wireless communication network and/or in a wirelesscommunication network. It may be envisioned that a node in or forcommunication, and/or in, of or for a wireless communication network isadapted for communication utilizing one or more RATs, in particularLTE/E-UTRA.

A communication may generally involve transmitting and/or receivingmessages, in particular in the form of packet data. A message or packetmay comprise control and/or configuration data and/or payload dataand/or represent and/or comprise a batch of physical layertransmissions. Control and/or configuration data may refer to datapertaining to the process of communication and/or nodes and/or terminalsof the communication. It may, e.g., include address data referring to anode or terminal of the communication and/or data pertaining to thetransmission mode and/or spectral configuration and/or frequency and/orcoding and/or timing and/or bandwidth as data pertaining to the processof communication or transmission, e.g. in a header. Each node orterminal involved in communication may comprise radio circuitry and/orcontrol circuitry and/or antenna circuitry, which may be arranged toutilize and/or implement one or more than one radio access technologies.

Radio circuitry of a node or terminal may generally be adapted for thetransmission and/or reception of radio waves, and in particular maycomprise a corresponding transmitter and/or receiver and/or transceiver,which may be connected or connectable to antenna circuitry and/orcontrol circuitry. Control circuitry of a node or terminal may comprisea controller and/or memory arranged to be accessible for the controllerfor read and/or write access. The controller may be arranged to controlthe communication and/or the radio circuitry and/or provide additionalservices. Circuitry of a node or terminal, in particular controlcircuitry, e.g. a controller, may be programmed to provide thefunctionality described herein. A corresponding program code may bestored in an associated memory and/or storage medium and/or be hardwiredand/or provided as firmware and/or software and/or in hardware. Acontroller may generally comprise a processor and/or microprocessorand/or microcontroller and/or FPGA (Field-Programmable Gate Array)device and/or ASIC (Application Specific Integrated Circuit) device.More specifically, it may be considered that control circuitry comprisesand/or may be connected or connectable to memory, which may be adaptedto be accessible for reading and/or writing by the controller and/orcontrol circuitry. Radio access technology may generally comprise, e.g.,Bluetooth and/or Wifi and/or WIMAX and/or cdma2000 and/or GERAN and/orUTRAN and/or in particular E-Utran and/or LTE. A communication may inparticular comprise a physical layer (PHY) transmission and/orreception, onto which logical channels and/or logical transmissionand/or receptions may be imprinted or layered.

A node of a wireless communication network may be implemented as aterminal and/or user equipment and/or network node and/or base station(e.g. eNodeB) and/or relay node and/or any device generally adapted forcommunication in a wireless communication network, in particularcellular communication.

A wireless communication network or cellular network may comprise anetwork node, in particular a radio network node, which may be connectedor connectable to a core network, e.g. a core network with an evolvednetwork core, e.g. according to LTE. A network node may e.g. be a basestation. The connection between the network node and the corenetwork/network core may be at least partly based on a cable/landlineconnection. Operation and/or communication and/or exchange of signalsinvolving part of the core network, in particular layers above a basestation or eNB, and/or via a predefined cell structure provided by abase station or eNB, may be considered to be of cellular nature or becalled cellular operation.

A terminal may be implemented as a user equipment; it may generally beconsidered that a terminal is adapted to provide and/or define an endpoint of a wireless communication and/or for a wireless communicationnetwork. A terminal or a user equipment (UE) may generally be a deviceconfigured for wireless device-to-device communication and/or a terminalfor a wireless and/or cellular network, in particular a mobile terminal,for example a mobile phone, smart phone, tablet, PDA, etc. A userequipment or terminal may be a node of or for a wireless communicationnetwork as described herein, e.g. if it takes over some control and/orrelay functionality for another terminal or node. It may be envisionedthat terminal or user equipment is adapted for one or more RATs, inparticular LTE/E-UTRA. It may be considered that a terminal or userequipment comprises radio circuitry and/control circuitry for wirelesscommunication. Radio circuitry may comprise for example a receiverdevice and/or transmitter device and/or transceiver device. Controlcircuitry may include a controller, which may comprise a microprocessorand/or microcontroller and/or FPGA (Field-Programmable Gate Array)device and/or ASIC (Application Specific Integrated Circuit) device. Itmay be considered that control circuitry comprises or may be connectedor connectable to memory, which may be adapted to be accessible forreading and/or writing by the controller and/or control circuitry. Itmay be considered that a terminal or user equipment is configured to bea terminal or user equipment adapted for LTE/E-UTRAN. Generally, aterminal may be adapted to support dual connectivity. It may comprisetwo independently operable transmitter (or transceiver) circuitriesand/or two independently operable receiver circuitries; for dualconnectivity, it may be adapted to utilize one transmitter (and/orreceiver or transceiver, if provided) for communication with a masternetwork node and one transmitter (and/or receiver or transceiver, ifprovided) for communication with a secondary network node. It may beconsidered that a terminal comprises more than two such independentlyoperable circuitries.

A network node or base station, e.g. an eNodeB, may be any kind of basestation of a wireless and/or cellular network adapted to serve one ormore terminals or user equipments. It may be considered that a basestation is a node or network node of a wireless communication network. Anetwork node or base station may be adapted to provide and/or defineand/or to serve one or more cells of the network and/or to allocatefrequency and/or time resources for communication to one or more nodesor terminals of a network. Generally, any node adapted to provide suchfunctionality may be considered a base station. It may be consideredthat a base station or more generally a network node, in particular aradio network node, comprises radio circuitry and/or control circuitryfor wireless communication. It may be envisioned that a base station ornetwork node is adapted for one or more RATs, in particular LTE/E-UTRA.Radio circuitry may comprise for example a receiver device and/ortransmitter device and/or transceiver device. Control circuitry mayinclude a controller, which may comprise a microprocessor and/ormicrocontroller and/or FPGA (Field-Programmable Gate Array) deviceand/or ASIC (Application Specific Integrated Circuit) device. It may beconsidered that control circuitry comprises or may be connected orconnectable to memory, which may be adapted to be accessible for readingand/or writing by the controller and/or control circuitry. A basestation may be arranged to be a node of a wireless communicationnetwork, in particular configured for and/or to enable and/or tofacilitate and/or to participate in cellular communication, e.g. as adevice directly involved or as an auxiliary and/or coordinating node.Generally, a base station may be arranged to communicate with a corenetwork and/or to provide services and/or control to one or more userequipments and/or to relay and/or transport communications and/or databetween one or more user equipments and a core network and/or anotherbase station. A network node or base station may generally be adapted toallocate and/or schedule time/frequency resources of a network and/orone or more cells serviced by the base station. An eNodeB (eNB) may beenvisioned as an example of a base station, e.g. according to an LTEstandard. It may be considered that a base station is configured as orconnected or connectable to an Evolved Packet Core (EPC) and/or toprovide and/or connect to corresponding functionality. The functionalityand/or multiple different functions of a base station may be distributedover one or more different devices and/or physical locations and/ornodes. A base station may be considered to be a node of a wirelesscommunication network. Generally, a base station may be considered to beconfigured to be a controlling node and/or coordinating node and/or toallocate resources in particular for cellular communication via one ormore than one cell.

It may be considered for cellular communication there is provided atleast one uplink (UL) connection and/or channel and/or carrier and atleast one downlink (DL) connection and/or channel and/or carrier, e.g.via and/or defining a cell, which may be provided by a network node, inparticular a base station or eNodeB. An uplink direction may refer to adata transfer direction from a terminal to a network node, e.g. basestation and/or relay station. A downlink direction may refer to a datatransfer direction from a network node, e.g. base station and/or relaynode, to a terminal. UL and DL may be associated to different frequencyresources, e.g. carriers and/or spectral bands. A cell may comprise atleast one uplink carrier and at least one downlink carrier, which mayhave different frequency bands.

A network node, e.g. a base station or eNodeB, may be adapted to provideand/or define and/or control one or more cells, e.g. a group of cells,which may be carrier aggregated (CA) cells. The group of cells maycomprise at least one primary cell, which may be considered to be amember of the group and/or to be associated to the group. The cell groupmay comprise one or more secondary cells (it should be noted that everygroup may comprise secondary cells, not only a secondary group; thesecondary in this context refers to being secondary to the primary cellof a group). A primary cell may be adapted and/or utilized for providingcontrol information (in particular allocation data, and/or schedulingand/or allocation information regarding the primary cell and/or thegroup of cells to and/or from a terminal connected for communication(transmission and reception) and/or configured with the cell. Thecontrol information may pertain to the primary cell and/or the group ofcells. Each primary cell and/or the associated group may be associatedto a specific network node. A master network node may be adapted toprovide and/or service and/or define a primary cell in a master cellgroup. A secondary network node may be adapted to provide and/or serviceand/or define a secondary cell group.

A terminal may be adapted to be configured with and/or to communicatevia master cell group (at least one primary cell) for communicating witha master network node. Additionally, a terminal may be adapted to beconfigured with and/or to communicate via secondary cell group (at leastone (secondary) primary cell) for communicating with a secondary networknode; the terminal may generally be adapted for dual connectivity. Theterminal may comprise suitable circuitry, e.g. a first transmitterand/or receiver and/or transceiver circuitry (e.g., for communicatingwith the master network node) and a second first transmitter and/orreceiver and/or transceiver circuitry (e.g., for communicating with thesecondary network node/s).

A network node, in particular a base station, and/or a terminal, inparticular a UE, may be adapted for communication in spectral bands(frequency bands) licensed and/or defined for LTE.

Resources or communication resources may generally be frequency and/ortime resources, which may comprises e.g. frames, subframes, slots,resource blocks, carriers, subcarriers, channels, frequency/spectralbands, etc. Allocated or scheduled resources may comprise and/or referto frequency-related information, in particular regarding one or morecarriers and/or bandwidth and/or subcarriers and/or time-relatedinformation, in particular regarding frames and/or slots and/orsubframes, and/or regarding resource blocks and/or time/frequencyhopping information. Transmitting on allocated resources and/orutilizing allocated resources may comprise transmitting data on theresources allocated, e.g. on the frequency and/or subcarrier and/orcarrier and/or timeslots or subframes indicated. It may generally beconsidered that allocated resources may be released and/or de-allocated.A network or a node of a network, e.g. a network node or allocationnode, e.g. a base station, may be adapted to determine and/or transmitcorresponding allocation or scheduling data, e.g. data indicatingrelease or de-allocation of resources and/or scheduling of UL and/or DLresources. Accordingly, resource allocation may be performed by thenetwork and/or by a network node; a network node adapted for providingresource allocation/scheduling for one or more than one terminals may beconsidered to be a controlling node. Resources may be allocated and/orscheduled on a cell level and/or by a network node servicing and/orproviding the cell.

Allocation data may be considered to be data indicating and/or grantingresources allocated by a network node, e.g. a controlling and/orallocation node, in particular data identifying or indicating whichresources are reserved or allocated, e.g. for cellular communication,which may generally comprise transmitting and/or receiving data and/orsignals; the allocation data may indicate a resource grant or releaseand/or resource scheduling. A grant or resource grant may be consideredto be one example of allocation data. It may be considered that anallocation node is adapted to transmit allocation data directly to anode and/or indirectly, e.g. via a relay node and/or another node orbase station. Allocation data may comprise control data and/or be partof or form a message, in particular according to a pre-defined format,for example a DCI format, which may be defined in a standard, e.g. LTE.In particular, allocation data may comprise information and/orinstructions to reserve resources or to release resources, which mayalready be allocated. A terminal may generally be adapted to performtransmission of data to, e.g. UL data, and/or reception of data from, anetwork node and/or to more than one network nodes, according toallocation data.

FIG. 5 schematically shows a user equipment 10. User equipment 10comprises control circuitry 20, which may comprise a controllerconnected to a memory. Any module of a user equipment may implemented inand/or executable by, user equipment, in particular the controlcircuitry 20. User equipment 10 also comprises radio circuitry 22providing receiving and transmitting or transceiving functionality, theradio circuitry 22 connected or connectable to the control circuitry. Anantenna circuitry 24 of the user equipment 10 is connected orconnectable to the radio circuitry 22 to collect or send and/or amplifysignals. Radio circuitry 22 and the control circuitry 20 controlling itare configured for cellular communication with a network on a firstcell/carrier and a second cell/carrier and/or for dual connectivity, inparticular utilizing E-UTRAN/LTE resources as described herein. The userequipment 10 may be adapted to carry out any of the methods foroperating a terminal disclosed herein; in particular, it may comprisecorresponding circuitry, e.g. control circuitry. The antenna circuitryand/or radio circuitry may be adapted to provide at least twoindependent transmitter circuitries and/or at least two independentreceiver circuitries, each of which may be associated or associatable toa different node for dual connectivity. The user equipment may beconfigured or configurable to associate such circuitry to a node, e.g.based on allocation data and/or control data provided by the networkand/or a network node.

FIG. 6 schematically show a network node or base station 100, which inparticular may be an eNodeB. Network node 100 comprises controlcircuitry 120, which may comprise a controller connected to a memory.Any module of a network node, e.g. a receiving module and/ortransmitting module and/or control or processing module and/orscheduling module, may be implemented in and/or executable by thenetwork node, in particular the control circuitry 120. The controlcircuitry 120 is connected to control radio circuitry 122 of the networknode 100, which provides receiver and transmitter and/or transceiverfunctionality. An antenna circuitry 124 may be connected or connectableto radio circuitry 122 for signal reception or transmittance and/oramplification. The network node 100 may be adapted to carry out any ofthe methods for operating a network node disclosed herein; inparticular, it may comprise corresponding circuitry, e.g. controlcircuitry.

FIG. 7 shows a flowchart of a method for operating a D2D enabled UE,which may be any D2D enabled UE as described herein. The method maycomprise an action TS10 of performing a cell search in an out ofcoverage condition of the UE. Performing a cell search is based on afirst measurement configuration during a first phase, and based on asecond measurement configuration during a second phase, wherein thefirst measurement configuration pertains to a carrier whose sidelink ispreconfigured for ProSe operation in out of network coverage operation.

FIG. 8 schematically shows a D2D enabled UE, which may be any D2Denabled UE as described herein. The D2D enabled UE comprises a cellsearch module TM10 for performing action TS10.

FIG. 9 shows a flowchart of a method for operating a network node, whichmay be any network node as described herein. The method comprises anaction NS10 of configuring a D2D enabled UE with a first measurementconfiguration, wherein the first measurement configuration pertains to acarrier whose sidelink is preconfigured for D2D operation in out ofnetwork coverage operation.

FIG. 10 schematically shows a network node, which may be any networknode as described herein. The network node comprises a configuringmodule NM10 for performing action NS10.

Generally, there may be considered a network node adapted for performingany one of the methods for operating a network node described herein.

There may be considered a user equipment adapted for performing any oneof the methods for operating a user equipment described herein.

There is also disclosed a program product comprising code executable bycontrol circuitry, the code causing the control circuitry to carry outand/or control any one of the method for operating a user equipment ornetwork node as described herein, in particular if executed on controlcircuitry, which may be control circuitry of a user equipment or anetwork node as described herein.

Moreover, there is disclosed a carrier medium arrangement carryingand/or storing at least any one of the program products described hereinand/or code executable by control circuitry, the code causing thecontrol circuitry to perform and/or control at least any one of themethods described herein. A carrier medium arrangement may comprise oneor more carrier media. Generally, a carrier medium may be accessibleand/or readable and/or receivable by control circuitry. Storing dataand/or a program product and/or code may be seen as part of carryingdata and/or a program product and/or code. A carrier medium generallymay comprise a guiding/transporting medium and/or a storage medium. Aguiding/transporting medium may be adapted to carry and/or carry and/orstore signals, in particular electromagnetic signals and/or electricalsignals and/or magnetic signals and/or optical signals. A carriermedium, in particular a guiding/transporting medium, may be adapted toguide such signals to carry them. A carrier medium, in particular aguiding/transporting medium, may comprise the electromagnetic field,e.g. radio waves or microwaves, and/or optically transmissive material,e.g. glass fiber, and/or cable. A storage medium may comprise at leastone of a memory, which may be volatile or non-volatile, a buffer, acache, an optical disc, magnetic memory, flash memory, etc.

A user equipment or terminal being configured with a cell, e.g. aserving cell, and/or carrier, and/or being connected to a network nodevia a cell, may be in a state in which it may communicate (transmitand/or receive data, e.g. with the network node) using the cell orcarrier, e.g. being registered with the network for communication and/orbeing synchronized to the cell and/or carrier; in particular, the cellmay be activated for the user equipment or terminal and/or the lattermay be in an RRC_connected or RRC_idle state regarding the cell or thenode providing the cell. A user equipment configured with a certainconfiguration may be set and/or operational according to theconfiguration; the configuration may be configured by a network and/ornetwork node, e.g. by transmitting corresponding information (theinformation may represent the configuration).

A user equipment or terminal may be adapted to perform an activationprocedure, in which it activates a cell based on a timing message and/ortiming parameter received from a network node providing and/or servicingand/or defining and/or scheduling the cell. The activation procedure maybe part of an access procedure, in particular a random access procedure.

An access procedure/request may generally be a random access procedureas described herein, e.g. with contention resolution or contention-free.It may be performed between a terminal and/or network node to accessand/or time align and/or activate a cell, for the terminal, the cellbeing provided and/or serviced and/or defined and/or controlled byand/or associated to the network node. An activation procedure maycomprise an access procedure. It should be noted that the result of aperformed access or activation procedure may be a failure, if theterminal was not able to activate the cell, e.g. due to unfavorablereception conditions.

Synchronization information may generally refer to information regardingthe time difference between signals from the master network node, e.g.via the MCG, and the secondary network node, e.g. via the SCG, and/or tothe time difference between signals received, by the terminal, via theMCG and the SCG, in particular via the respective primary cells (PCelland PSCell). Synchronization information may refer and/or comprise asynchronization level. A synchronization level may indicate whether thetime difference (or its absolute value) lies above a given thresholdand/or between given thresholds, e.g. if it is larger than a thresholddefining the signals of being synchronized. Generally, a synchronizationlevel may indicate a pre-defined type or mode of synchronization in dualconnectivity, as discussed herein. One or more thresholds may be definedas above in terms of types of synchronization. Synchronizationinformation may additionally or alternatively comprise the value and/orabsolute value of the time difference.

Configuring a terminal or UE, e.g. by a network or network node, maycomprise transmitting, by the network or network node, one or moreparameters and/or commands and/or allocation or control data to theterminal or UE, and/or the terminal or UE changing its configurationand/or setup, e.g. based on received parameters and/or commands and/orallocation data from the network and/or the network node.

In the context of this description, wireless communication may becommunication, in particular transmission and/or reception of data, viaelectromagnetic waves and/or an air interface, in particular radiowaves, e.g. in a wireless communication network and/or utilizing a radioaccess technology (RAT). The communication may involve one or more thanone terminal connected to a wireless communication network and/or morethan one node of a wireless communication network and/or in a wirelesscommunication network. It may be envisioned that a node in or forcommunication, and/or in, of or for a wireless communication network isadapted for communication utilizing one or more RATs, in particularLTE/E-UTRA. A communication may generally involve transmitting and/orreceiving messages, in particular in the form of packet data. A messageor packet may comprise control and/or configuration data and/or payloaddata and/or represent and/or comprise a batch of physical layertransmissions. Control and/or configuration data may refer to datapertaining to the process of communication and/or nodes and/or terminalsof the communication. It may, e.g., include address data referring to anode or terminal of the communication and/or data pertaining to thetransmission mode and/or spectral configuration and/or frequency and/orcoding and/or timing and/or bandwidth as data pertaining to the processof communication or transmission, e.g. in a header. Each node orterminal involved in communication may comprise radio circuitry and/orcontrol circuitry and/or antenna circuitry, which may be arranged toutilize and/or implement one or more than one radio access technologies.Radio circuitry of a node or terminal may generally be adapted for thetransmission and/or reception of radio waves, and in particular maycomprise a corresponding transmitter and/or receiver and/or transceiver,which may be connected or connectable to antenna circuitry and/orcontrol circuitry. Control circuitry of a node or terminal may comprisea controller and/or memory arranged to be accessible for the controllerfor read and/or write access. The controller may be arranged to controlthe communication and/or the radio circuitry and/or provide additionalservices.

Circuitry of a node or terminal, in particular control circuitry, e.g. acontroller, may be programmed to provide the functionality describedherein. A corresponding program code may be stored in an associatedmemory and/or storage medium and/or be hardwired and/or provided asfirmware and/or software and/or in hardware. A controller may generallycomprise a processor and/or microprocessor and/or microcontroller and/orFPGA (Field-Programmable Gate Array) device and/or ASIC (ApplicationSpecific Integrated Circuit) device. More specifically, it may beconsidered that control circuitry comprises and/or may be connected orconnectable to memory, which may be adapted to be accessible for readingand/or writing by the controller and/or control circuitry. Radio accesstechnology may generally comprise, e.g., Bluetooth and/or Wifi and/orWIMAX and/or cdma2000 and/or GERAN and/or UTRAN and/or in particularE-Utran and/or LTE. A communication may in particular comprise aphysical layer (PHY) transmission and/or reception, onto which logicalchannels and/or logical transmission and/or receptions may be imprintedor layered.

In the context of this description, wireless communication may becommunication, in particular transmission and/or reception of data, viaelectromagnetic waves and/or an air interface, in particular radiowaves, e.g. in a wireless communication network and/or utilizing a radioaccess technology (RAT). The communication may be between nodes of awireless communication network and/or in a wireless communicationnetwork. It may be envisioned that a node in or for communication,and/or in, of or for a wireless communication network is adapted for,and/or for communication utilizing, one or more RATs, in particularLTE/E-UTRA. A communication may generally involve transmitting and/orreceiving messages, in particular in the form of packet data. A messageor packet may comprise control and/or configuration data and/or payloaddata and/or represent and/or comprise a batch of physical layertransmissions. Control and/or configuration data may refer to datapertaining to the process of communication and/or nodes of thecommunication. It may, e.g., include address data referring to a node ofthe communication and/or data pertaining to the transmission mode and/orspectral configuration and/or frequency and/or coding and/or timingand/or bandwidth as data pertaining to the process of communication ortransmission, e.g. in a header. Each node involved in such communicationmay comprise radio circuitry and/or control circuitry and/or antennacircuitry, which may be arranged to utilize and/or implement one or morethan one radio access technologies.

Radio circuitry of a node may generally be adapted for the transmissionand/or reception of radio waves, and in particular may comprise acorresponding transmitter and/or receiver and/or transceiver, which maybe connected or connectable to antenna circuitry and/or controlcircuitry. Control circuitry of a node may comprise a controller and/ormemory arranged to be accessible for the controller for read and/orwrite access. The controller may be arranged to control thecommunication and/or the radio circuitry and/or provide additionalservices. Circuitry of a node, in particular control circuitry, e.g. acontroller, may be programmed to provide the functionality describedherein. A corresponding program code may be stored in an associatedmemory and/or storage medium and/or be hardwired and/or provided asfirmware and/or software and/or in hardware. A controller may generallycomprise a processor and/or microprocessor and/or microcontroller and/orFPGA (Field-Programmable Gate Array) device and/or ASIC (ApplicationSpecific Integrated Circuit) device. More specifically, it may beconsidered that control circuitry comprises and/or may be connected orconnectable to memory, which may be adapted to be accessible for readingand/or writing by the controller and/or control circuitry. Radio accesstechnology may generally comprise, e.g., Bluetooth and/or Wifi and/orWIMAX and/or cdma2000 and/or GERAN and/or UTRAN and/or in particularE-Utran and/or LTE. A communication may in particular comprise aphysical layer (PHY) transmission and/or reception, onto which logicalchannels and/or logical transmission and/or receptions may be imprintedor layered. A node of a wireless communication network may beimplemented as a D2D device and/or user equipment and/or base stationand/or relay node and/or any device generally adapted fordevice-to-device communication. A wireless communication network maycomprise at least one of a device configured for device-to-devicecommunication, a D2D device, and/or a user equipment and/or base stationand/or relay node, in particular at least one user equipment, which maybe arranged for device-to-device communication with a second D2D deviceor node of the wireless communication network, in particular with asecond user equipment.

A node of or for a wireless communication network may generally be awireless device configured for wireless device-to-device communication,in particular using the frequency spectrum of a cellular and/or wirelesscommunications network, and/or frequency and/or time resources of such anetwork. Device-to-device communication may optionally include broadcastand/or multicast communication to a plurality of devices or nodes. Acellular network may comprise a network node, in particular a radionetwork node, which may be connected or connectable to a core network,e.g. a core network with an evolved network core, e.g. according to LTE.The connection between the network node and the core network/networkcore may be at least partly based on a cable/landline connection.Operation and/or communication and/or exchange of signals involving partof the core network, in particular layers above a base station or eNB,and/or via a predefined cell structure provided by a base station oreNB, may be considered to be of cellular nature or be called cellularoperation. Operation and/or communication and/or exchange of signalswithout involvement of layers above a base station and/or withoututilizing a predefined cell structure provided by a base station or eNB,may be considered to be D2D communication or operation, in particular,if it utilizes the radio resources, in particular carriers and/orfrequencies, and/or equipment (e.g. circuitry like radio circuitryand/or antenna circuitry, in particular transmitter and/or receiverand/or transceiver) provided and/or used for cellular operation.

A user equipment (UE) may generally be a device configured for wirelessdevice-to-device communication (it may be a D2D device) and/or aterminal for a wireless and/or cellular network, in particular a mobileterminal, for example a mobile phone, smart phone, tablet, PDA, etc. Auser equipment may be a node of or for a wireless communication networkas described herein. It may be envisioned that a user equipment or D2Ddevice is adapted for one or more RATs, in particular LTE/E-UTRA. A userequipment may generally be proximity services (ProSe) enabled, which maymean it is D2D capable or enabled. It may be considered that a userequipment comprises radio circuitry and/control circuitry for wirelesscommunication. Radio circuitry may comprise for example a receiverdevice and/or transmitter device and/or transceiver device. Controlcircuitry may include a controller, which may comprise a microprocessorand/or microcontroller and/or FPGA (Field-Programmable Gate Array)device and/or ASIC (Application Specific Integrated Circuit) device. Itmay be considered that control circuitry comprises or may be connectedor connectable to memory, which may be adapted to be accessible forreading and/or writing by the controller and/or control circuitry. Anode or device of or for a wireless communication network may generallybe a user equipment or D2D device. It may be considered that a userequipment is configured to be a user equipment adapted for and/oraccording to LTE/E-UTRAN.

A base station may be any kind of base station of a wireless and/orcellular network adapted to serve one or more user equipments. It may beconsidered that a base station is a node of a wireless communicationnetwork. A base station may be adapted to provide and/or define one ormore cells of the network and/or to allocate or schedule frequencyand/or time resources for communication to one or more nodes of anetwork, in particular UL resources, for example for device-to-devicecommunication, which may be communication between devices different fromthe base station. Generally, any node adapted to provide suchfunctionality may be considered a base station. It may be consideredthat a base station or more generally a network node, in particular aradio network node, comprises radio circuitry and/or control circuitryfor wireless communication. It may be envisioned that a base station ornetwork node is adapted for one or more RATs, in particular LTE/E-UTRA.Radio circuitry may comprise for example a receiver device and/ortransmitter device and/or transceiver device. Control circuitry mayinclude a controller, which may comprise a microprocessor and/ormicrocontroller and/or FPGA (Field-Programmable Gate Array) deviceand/or ASIC (Application Specific Integrated Circuit) device. It may beconsidered that control circuitry comprises or may be connected orconnectable to memory, which may be adapted to be accessible for readingand/or writing by the controller and/or control circuitry. A basestation may be arranged to be a node of a wireless communicationnetwork, in particular configured for and/or to enable and/or tofacilitate and/or to participate in device-to-device communication, e.g.as a device directly involved or as an auxiliary and/or coordinatingnode. Generally, a base station may be arranged to communicate with acore network and/or to provide services and/or control to one or moreuser equipments and/or to relay and/or transport communications and/ordata between one or more user equipments and a core network and/oranother base station and/or be Proximity Service enabled. An eNodeB(eNB) may be envisioned as an example of a base station, in particularaccording to LTE. A base station may generally be proximity serviceenabled and/or to provide corresponding services. It may be consideredthat a base station is configured as or connected or connectable to anEvolved Packet Core (EPC) and/or to provide and/or connect tocorresponding functionality. The functionality and/or multiple differentfunctions of a base station may be distributed over one or moredifferent devices and/or physical locations and/or nodes. A base stationmay be considered to be a node of a wireless communication network.Generally, a base station may be considered to be configured to be acontrolling node and/or to allocate resources in particular fordevice-to-device communication between two nodes of a wirelesscommunication network, in particular two user equipments.

A storage medium may be adapted to store data and/or store instructionsexecutable by control circuitry and/or a computing device, theinstruction causing the control circuitry and/or computing device tocarry out and/or control any one of the methods described herein whenexecuted by the control circuitry and/or computing device. A storagemedium may generally be computer-readable, e.g. an optical disc and/ormagnetic memory and/or a volatile or non-volatile memory and/or flashmemory and/or RAM and/or ROM and/or EPROM and/or EEPROM and/or buffermemory and/or cache memory and/or a database.

Resources or communication resources may generally be frequency and/ortime resources. Allocated or scheduled resources may comprise and/orrefer to frequency-related information, in particular regarding one ormore carriers and/or bandwidth and/or subcarriers and/or time-relatedinformation, in particular regarding frames and/or slots and/orsubframes, and/or regarding resource blocks and/or time/frequencyhopping information. Allocated resources may in particular refer to ULand/or DL resources, e.g. UL resources for UE to transmit. Transmittingon allocated resources and/or utilizing allocated resources may comprisetransmitting data on the resources allocated, e.g. on the frequencyand/or subcarrier and/or carrier and/or timeslots or subframesindicated. It may generally be considered that allocated resources maybe released and/or de-allocated. A network or a node of a network, e.g.an allocation or controlling or serving node, may be adapted todetermine and/or transmit corresponding allocation data indicatingrelease or de-allocation of resources to one or more UE. Accordingly,resource allocation may be performed by the network and/or by a node, inparticular a node within and/or within a cell of a cellular networkcovering a UE participating or intending to participate in dualconnectivity. In dual connectivity, more than one node may be a servingand/or controlling node, providing allocation data regarding theresources utilized for communication between itself and the UE.

Allocation data may be considered to be data indicating and/or grantingresources allocated by the allocation node, in particular dataidentifying or indicating which resources are reserved or allocated forcommunication for a UE and/or which resources a UE may use forcommunication and/or data indicating a resource grant or release. Agrant or resource grant may be considered to be one example ofallocation data. It may be considered that an allocation node is adaptedto transmit allocation data directly to a node and/or indirectly, e.g.via a relay node and/or another node or base station. Allocation datamay comprise control data and/or be part of or form a message, inparticular according to a pre-defined format, for example a DCI format,which may be defined in a standard, e.g. LTE. In particular, allocationdata may comprise information and/or instructions to reserve resourcesor to release resources, which may already be allocated. Generally,allocation data may indicate and/or instruct transmission mode and/orconfiguration, in particular regarding a power level of transmission. AUE may generally be adapted for configuring itself according toallocation data, in particular to set a corresponding power level and/ortiming of UL and DL operations.

A network device or node and/or a user equipment may be or comprise asoftware/program arrangement arranged to be executable by a hardwaredevice, e.g. control circuitry, and/or storable in a memory, which mayprovide dual connectivity functionality and/or corresponding controlfunctionality and/or control functionality to carry out any one of themethods described herein and/or to implement any one or more than onefunctionalities of a user equipment and/or network node describedherein.

Radio spectrum: Although at least some of the embodiments may bedescribed for D2D transmissions in the UL spectrum (FDD) or UL resources(TDD), the embodiments are not limited to the usage of UL radioresources, neither to licensed or unlicensed spectrum, or any specificspectrum at all.

A cellular network or mobile or wireless communication network maycomprise e.g. an LTE network (FDD or TDD), UTRA network, CDMA network,WiMAX, GSM network, any network employing any one or more radio accesstechnologies (RATs) for cellular operation. The description herein isgiven for LTE, but it is not limited to the LTE RAT.

RAT (radio access technology) may generally include: e.g. LTE FDD, LTETDD, GSM, CDMA, WCDMA, WiFi, WLAN, WiMAX, etc.

A measurement gap may refer to a time gap or interval, in which notransmission and reception happens, in particular regarding a servingcell or a given carrier. Since there is no signal transmission andreception during the gap (at least in the serving cell or givencarrier), a D2D device or UE can switch to another or a target cell orcarrier and/or perform a measurement on the target cell or carrier, e.g.for signal quality, utilizing the same receiver.

The term “intra-frequency” may refer to issued related to the samefrequency/bandwith and/or carrier, e.g. between neighboring cells (whichmay be provided by different BSs) having the same frequencies available.The term “inter-frequency” may refer to issues related to differentfrequencies/bandwidths and/or carriers, e.g. between different carriersin a multi-carrier arrangement.

A receiving operation may comprise a measurement operation, e.g. asignal quality measurement, which may be performed in a measurement gap,in which a receiver switching to a carrier/frequency to be measured maybe performed.

A network node may be a radio network node (which may be adapted forwireless or radio communication, e.g. with a UE) or another networknode. A network node generally may be a controlling node. Some examplesof a radio network node or controlling node are a radio base station, inparticular an eNodeB, a relay node, an access point, a cluster head,RNC, etc. The radio network node may be comprised in a mobilecommunication network and may support and/or be adapted for cellularoperation or communication and/or D2D operation or communication. Anetwork node, in particular a radio network node, may comprise radiocircuitry and/or control circuitry, in particular for wirelesscommunication. Some examples of a network node, which is not a radionetwork node, may comprise: a core network node, MME, a node controllingat least in part mobility of a wireless device, SON node, O&M node,positioning node, a server, an application server, an external node, ora node comprised in another network. Any network node may comprisecontrol circuitry and/or a memory. A network node may be considered tobe serving a node or UE, if it provides a cell of a cellular network(which may be called serving cell) to the served node or UE and/or isconnected or connectable to the UE via and/or for transmission and/orreception and/or UL and/or DL data exchange or transmission and/or ifthe network node is adapted to provide the UE with allocation and/orconfiguration data and/or a measurement performance characteristicand/or to configure the D2D device or UE.

Multiple carrier frequencies or functionality may refer to any of:different carrier frequencies within the same frequency band or withindifferent frequency bands, same PLMN or different PLMNs, same RAT ordifferent RATs. D2D operation may or may not occur on dedicated carrierfrequencies. DL and UL carrier frequencies in FDD are also examples ofdifferent carrier frequencies.

A frequency band herein may be FDD, TDD, HD-FDD, or unidirectional(e.g., DL-only band such as Band 29, in some examples). Multiple carrierfunctionality may include carrier aggregation functionality, in whichmultiple carriers or cells are used for transmission and/or receptionbetween two participants of communication. The carriers may becontinuous in the spectrum or discontinuous.

Each or any one of the network nodes or user equipments shown in thefigures may be adapted to perform the methods to be carried out by auser equipment described herein. Alternatively or additionally, each orany of the user equipments shown in the figures may comprise any one orany combination of the features of a user equipment described herein.Each or any one of the network nodes or controlling nodes or eNBs orbase stations shown in the figures may be adapted to perform the methodsto be carried out by network node or base station described herein.Alternatively or additionally, the each or any one of the controlling ornetwork nodes or eNBs or base stations shown in the figures may compriseany one or any one combination of the features of a network node or eNBor base station described herein.

Some useful abbreviations comprise

Abbreviation Explanation DCI Downlink Control Information eNB evolvedNodeB, base station TTI Transmission-Time Interval UE User Equipment ULUplink DRS Discovery Reference Signal SCell Secondary Cell SRS SoundingReference Signal PCFICH Physical Control Format Indicator Channel PDCCHPhysical Downlink Control Channel PUSCH Physical Uplink Shared ChannelPUCCH Physical Uplink Control Channel RRM Radio Resource Management CISTransmission Confirmation Signal ACK Acknowledged ADC Analog-to-digitalconversion AGC Automatic gain control ANR Automatic neighbor relationsBCH Broadcast channel BLER Block error rate BS Base station BSC Basestation controller BTS Base transceiver station CA Carrier aggregationCC Component carrier CG Cell group CGI Cell global identity CP Cyclicprefix CPICH Common pilot channel CSG Closed subscriber group DASDistributed antenna system DC Dual connectivity DFT Discrete FourierTransform DL Downlink DL-SCH Downlink shared channel DRX Discontinuousreception EARFCN Evolved absolute radio frequency channel number ECGIEvolved CGI eNB eNodeB FDD Frequency division duplex FFT Fast Fouriertransform HD-FDD Half duplex FDD HO Handover M2M machine to machine MACMedia access control MCG Master cell group MDT Minimization of drivetests MeNB Master eNode B MME Mobility management entity MRTD Maximumreceive timing difference MSR Multi-standard radio NACK Not acknowledgedOFDM Orthogonal frequency division multiplexing SI System InformationPCC Primary component carrier PCI Physical cell identity PCell PrimaryCell PCG Primary Cell Group PCH Paging channel PDU Protocol data unitPGW Packet gateway PHICH Physical HARQ indication channel PLMN Publicland mobile network PSCell Primary SCell PSC Primary serving cell PSSPrimary synchronization signal RAT Radio Access Technology RF Radiofrequency RLM Radio link monitoring RNC Radio Network Controller RRCRadio resource control RRH Remote radio head RRU Remote radio unit RSCPReceived signal code power RSRP Reference Signal Received Power RSRQReference Signal Received Quality RSSI Received signal strengthindication RSTD Reference signal time difference SCC Secondary componentcarrier SCell Secondary Cell SCG Secondary Cell Group SeNB SecondaryeNode B SFN System frame number SGW Signaling gateway SINR Signal tointerference and noise ratio SON Self-organizing networks SSC Secondaryserving cell SSS Secondary synchronization signal TA Timing advance TAGTiming advance group TDD Time division duplex Tx Transmitter UARFCN UMTSAbsolute Radio Frequency Channel Number UE User equipment 3GPP 3^(rd)Generation Partnership Project Ack/NackAcknowledgment/Non-Acknowledgement, also A/N AP Access point BER/BLERBit Error Rate, BLock Error Rate; BS Base Station CA Carrier AggregationCC component carrier (a carrier in a carrier aggregate) CoMP CoordinatedMultiple Point Transmission and Reception CQI Channel QualityInformation CRS Cell-specific Reference Signal CSI Channel StateInformation CSI-RS CSI reference signal D2D Device-to-device DL DownlinkEPDCCH Enhanced Physical DL Control Channel DL Downlink; generallyreferring to transmission of data to a node/into a direction furtheraway from network core (physically and/or logically); in particular froma base station or eNodeB to a D2D enabled node or UE; often usesspecified spectrum/bandwidth/band different from UL (e.g. LTE FDD) eNBevolved NodeB; a form of base station, also called eNodeB E-UTRA/NEvolved UMTS Terrestrial Radio Access/ Network, an example of a RAT f1,f2, f3, . . . , fn carriers/carrier frequencies; different numbers mayindicate that the referenced carriers/ frequencies are different f1_UL,. . . , fn_UL Carrier for Uplink/in Uplink frequency or band f1_DL, . .. , fn_DL Carrier for Downlink/in Downlink frequency or band FDDFrequency Division Duplexing ID Identity L1 Layer 1 L2 Layer 2 LTE LongTerm Evolution, a telecommunications standard MAC Medium Access ControlMBSFN Multiple Broadcast Single Frequency Network MDT Minimisation ofDrive Test MME Mobility Management Entity; a control entity of awireless communication network (LTE) providing control functionalitye.g. for radio network nodes like eNBs NW Network OFDM OrthogonalFrequency Division Multiplexing O&M Operational and Maintenance OSSOperational Support Systems PC Power Control PCell Primary Cell (e.g. inCA, in particular a primary cell of a Master Cell Group) PDCCH PhysicalDL Control Channel PH Power Headroom PHR Power Headroom Report Pscellprimary cell of a secondary cell group PSS Primary SynchronizationSignal PUSCH Physical Uplink Shared Channel R1, R2, . . . , RnResources, in particular time-frequency resources, in particularassigned to corresponding carrier f1, f2, . . . , fn RA Random AccessRACH Random Access Channel RAN Radio Access Network RAT Radio AccessTechnology RE Resource Element RB Resource Block RRH Remote radio headRRM Radio Resource Management RRU Remote radio unit RSRQ Referencesignal received quality RSRP Reference signal received power RSSIReceived signal strength indicator RX reception/receiver,reception-related SA Scheduling Assignment SCell Secondary Cell (e.g. inCA) SINR/SNR Signal-to-Noise-and-Interference Ratio; Signal-to- NoiseRatio SFN Single Frequency Network SON Self Organizing Network SSSSecondary Synchronization Signal TPC Transmit Power Control TXtransmission/transmitter, transmission-related TDD Time DivisionDuplexing UE User Equipment UL Uplink; generally referring totransmission of data to a node/into a direction closer to a network core(physically and/or logically); in particular from a D2D enabled node orUE to a base station or eNodeB; in the context of D2D, it may refer tothe spectrum/bandwidth/band utilized for transmitting in D2D, which maybe the same used for UL communication to a eNB in cellularcommunication; in some D2D variants, transmission by all devicesinvolved in D2D communication may in some variants generally be in ULspectrum/bandwidth/carrier/frequency DC Dual Connectivity MCG Main CellGroup SCG Secondary Cell Group PCell Primary Cell PSCell Primary SCellSCell Secondary Cell RACH Random Access Channel MeNB Master eNodeB SeNBSecondary eNodeB pSCell Primary SCell PCC Primary component carrier PCIPhysical cell identity PSS Primary synchronization signal RAT RadioAccess Technology RRC Radio resource control RSCP Received signal codepower RSRP Reference Signal Received Power RSRQ Reference SignalReceived Quality RSSI Received signal strength indication SCC Secondarycomponent carrier SIB System information block SON Self-organizingnetworks SSS Secondary synchronization signal TDD Time division duplexUARFCN UMTS Absolute Radio Frequency Channel Number HO Handover UE Userequipment RNC Radio Network Controller BSC Base station Controller PCellPrimary Cell SCell Secondary Cell

These and other abbreviations may be used according to LTE standarddefinitions.

In this description, for purposes of explanation and not limitation,specific details are set forth (such as particular network functions,processes and signaling steps) in order to provide a thoroughunderstanding of the technique presented herein. It will be apparent toone skilled in the art that the present concepts and aspects may bepracticed in other embodiments and variants that depart from thesespecific details. For example, the concepts and variants are partiallydescribed in the context of Long Term Evolution (LTE) or LTE-Advanced(LTE-A) mobile or wireless communications technologies; however, thisdoes not rule out the use of the present concepts and aspects inconnection with additional or alternative mobile communicationtechnologies such as the Global System for Mobile Communications (GSM).While the following embodiments will partially be described with respectto certain Technical Specifications (TSs) of the Third GenerationPartnership Project (3GPP), it will be appreciated that the presentconcepts and aspects could also be realized in connection with differentPerformance Management (PM) specifications.

Moreover, those skilled in the art will appreciate that the services,functions and steps explained herein may be implemented using softwarefunctioning in conjunction with a programmed microprocessor, or using anApplication Specific Integrated Circuit

(ASIC), a Digital Signal Processor (DSP), a Field Programmable GateArray (FPGA) or general purpose computer. It will also be appreciatedthat while the embodiments described herein are elucidated in thecontext of methods and devices, the concepts and aspects presentedherein may also be embodied in a program product as well as in a systemcomprising control circuitry, e.g. a computer processor and a memorycoupled to the processor, wherein the memory is encoded with one or moreprograms or program products that execute the services, functions andsteps disclosed herein.

It is believed that the advantages of the aspects and variants presentedherein will be fully understood from the foregoing description, and itwill be apparent that various changes may be made in the form,constructions and arrangement of the exemplary aspects thereof withoutdeparting from the scope of the concepts and aspects described herein orwithout sacrificing all of its advantageous effects. Because the aspectspresented herein can be varied in many ways, it will be recognized thatany scope of protection should be defined by the scope of the claimsthat follow without being limited by the description.

A serving carrier may be a carrier associated to a serving cell.

A carrier may generally refer to a frequency band or bandwidth availablefor communication, e.g. according to a standard like LTE. A carrier maybe divided into subcarriers.

It may be considered that for FDD, a carrier is allocated and/or used(only) for UL communication or DL communication. There may be defined(e.g. by a standard like LTE) and/or configured or chosen (e.g., by anetwork node like an eNodeB according to a standard) combinations ofcarriers (pair bands) comprising one UL carrier and at least one DLcarrier in combination for FDD. Thus, for each UL carrier, there may beat least one associated DL carrier. For TDD, a carrier may be used forUL and DL communication, depending on allocation, such that the carriermay be shared for both directions. For D2D, a carrier (carriers)designated for UL may be used or configured (for or of a sidelink).Thus, in FDD, a sidelink whose carrier is preconfigured for D2D maycomprise an UL carrier which is used for D2D operation, and anassociated DL carrier, which may be associated to a cell and/or be usedfor control signaling, but generally may not necessarily be used for D2Doperation (it may not be used at all when the UL carrier is allocatedfor D2D operation). In TDD, a sidelink whose carrier is preconfiguredfor D2D may comprise one carrier, which may be carrier available for ULand DL for cellular communication (if allocated accordingly, e.g.time-shared with D2D operation), e.g. according to a standard like LTE.Carrier aggregation utilizing a plurality of the sidelink types,respectively associated carrier types, described herein may beconsidered.

It should be noted that in the above, depending on the application orembodiment referred to, a reference to a time or time difference, e.g.T1, delta1 or delta2, may identify a time threshold or an elapsed timesince a certain time reference, e.g. a time when the elapsed timestarted to be measure or run. From the context of the respectivedisclosure it is believed to be clear which interpretation of thereference is valid.

A cell search may general refer to searching for and/or identifying acell of a cellular network.

A carrier whose sidelink is preconfigured for D2D or ProSe operation inout of network coverage operation may comprise and/or refer to a carrierthe UE has been configured with for using for D2D operation specificallyfor OON situations, and/or while being in network coverage and/or beforeleaving network coverage. The configuration may be according to astandard (e.g., for carriers specifically for OON situations), and/or beconfigured by a network node, e.g. eNodeB, while in coverage with thateNodeB.

A measurement configuration pertaining to a carrier may be considered toindicate that a cell search is to be performed on the carrier. Ameasurement configuration generally may indicate and/or compriseindication/s or parameter/s used for measurements, in particular in thecontext of cell search, e.g. a carrier, and optionally power-relatedindications/s or parameter/s and/or timing or synchronization-relatedindications/s or parameter/s and/or modulation and/or encoding-relatedindications/s or parameter/s, and/or information/indication/s orparameter/s pertaining to the phase during which the measurementconfiguration is valid/to be used for cell search.

Preconfiguring a D2D enabled UE may pertain to the UE having informationpertaining and/or indicating the preconfigured carrier or configuration(in particular, a carrier and/or measurement configuration) in a memory,e.g. according to a standard and/or based on configuring performed by anetwork node, e.g. in advance and/or before entering the OOC condition.

The invention claimed is:
 1. A method for operating a Device-to-Device, D2D enabled User Equipment, UE, for a cellular communication network, the method comprising performing a cell search in an out of coverage condition of the UE, wherein performing a cell search is based on a first measurement configuration during a first phase, and based on a second measurement configuration during a second phase, wherein the first measurement configuration pertains to a carrier whose sidelink is preconfigured for Proximity Services, ProSe, operation in out of network coverage operation and wherein a first set of carriers that are searched based on the first measurement configuration during the first phase comprises less than all of a second set of carriers that are searched based on the second measurement configuration during the second phase.
 2. The method of claim 1 wherein the second phase is not performed if the UE detects a cell during the first phase.
 3. A Device-to-Device, D2D enabled User Equipment, UE, for a cellular communication network, the D2D enabled UE being adapted for performing a cell search in an out of coverage condition of the UE, wherein performing a cell search is based on a first measurement configuration during a first phase, and performing a cell search is based on a second measurement configuration during a second phase, wherein the first measurement configuration pertains to a carrier whose sidelink is preconfigured for D2D operation in out of network coverage operation and wherein a first set of carriers that are searched based on the first measurement configuration during the first phase comprises less than all of a second set of carriers that are searched based on the second measurement configuration during the second phase.
 4. The D2D enabled UE of claim 3 wherein the second phase is not performed if the UE detects a cell during the first phase.
 5. A method for operating a network node for a wireless communication network, the method comprising configuring a Device-to-Device, D2D, enabled User Equipment, UE, with a first measurement configuration for performing a cell search during a first phase and a second measurement configuration for performing a cell search during a second phase, wherein the first measurement configuration pertains to a carrier whose sidelink is preconfigured for D2D operation in out of network coverage operation and wherein a first set of carriers that are searched based on the first measurement configuration during the first phase comprises less than all of a second set of carriers that are searched based on the second measurement configuration during the second phase.
 6. A network node for a wireless communication network, the network node being adapted for configuring a Device-to-Device, D2D, enabled User Equipment, UE, with a first measurement configuration for performing a cell search during a first phase and a second measurement configuration for performing a cell search during a second phase, wherein the first measurement configuration pertains to a carrier whose sidelink is preconfigured for D2D operation in out of network coverage operation and wherein a first set of carriers that are searched based on the first measurement configuration during the first phase comprises less than all of a second set of carriers that are searched based on the second measurement configuration during the second phase. 